Terms from Nonpartisan League to Paramedic
- Nonpartisan League
- Nonsense Verse
- Noorderkwartier (Eng Northern Quarter)
- Noordse Compagnie (Eng ‘Northern Company’)
- Nootka
- Nora Kaye Biography (1920–87) (originally Nora Koreff)
- Nora Stanton Barney Biography (1883–1971) (née Blatch)
- Noradrenaline (UK) (/ norepinephrine (US) [naw(r)epinefrin])
- Norbert Rillieux Biography (1806–94)
- Norbert Wiener Biography (1894–1964)
- Norddeutscher Bund
- Norfolk (UK)
- Norfolk (USA)
- Norfolk Island
- Norm-referenced Test
- Norma ((Lat ‘level’))
- Norman (Abraham) Haskell Biography (1905–70)
- Norman (Adrian) Malcolm Biography (1911–90)
- Norman (Alexander) MacCaig Biography (1910–96)
- Norman (David) Willis Biography (1933– )
- Norman (Edward) Shumway Biography (1923–2006)
- Norman (Ernest) Borlaug Biography (1914– )
- Norman (George) Douglas Biography (1868–1952)
- Norman (Kingsley) Mailer Biography (1923– ) (originally Nachum Malech Mailer)
- Norman (Mattoon) Thomas Biography (1884–1968)
- Norman (Milton) Lear Biography (1922– )
- Norman (Percevel) Rockwell Biography (1894–1978)
- Norman (René) Del Mar Biography (1919–94)
- Norman Architecture
- Norman Bel Geddes Biography (1893–1958)
- Norman Bethune Biography (1899–1939)
- Norman Conquest
- Norman Cousins Biography (?1915–90)
- Norman Dello Joio Biography (1913– )
- Norman Dennis Newell Biography (1909– )
- Norman Dorsen Biography (1930– )
- Norman Eric Kirk Biography (1923–74)
- Norman Granz Biography (1918–2001)
- Norman Hammond Biography (1944– )
- Norman Hapgood Biography (1868–1937)
- Norman L(evi) Bowen Biography (1887–1956)
- Norman Lamm Biography (1927– )
- Norman Lindsay Biography (1879–1969)
- Norman Luboff Biography (1917–87)
- Norman Parkinson Biography (1913–90) (originally Ronald William Parkinson Smith)
- Norman Scott Biography (1889–1942)
- Norman Vincent Peale Biography (1898–1993)
- Norman Wingate Pirie Biography (1907–97)
- Normandy (Fr Normandie)
- Normandy Campaign
- Normandy, House Of
- Normans
- Norns
- Norris (Dewar) McWhirter Biography (1925–2004)
- Norrköping
- North African Campaign
- North America
- North American Free Trade Agreement (NAFTA)
- North Cape (Norwegian Nordkapp)
- North Carolina
- North Dakota
- North Downs Way
- North German Confederation
- North India, Church Of
- North Island
- North Sea
- North Sea Oil
- North West
- North West Company
- North York Moors
- North-West Rebellion
- Northallerton
- Northampton
- Northamptonshire
- Northeast Passage
- Northern Cape
- Northern Ireland (also Ulster)
- Northern Ireland Assembly
- Northern Province (renamed Limpopo (Feb 2002))
- Northern Territory
- Northing
- Northumberland
- Northumberland National Park
- Northumbria
- Northwest Coast Indians
- Northwest Frontier
- Northwest Passage
- Northwest Territories
- Norton (David) Zinder Biography (1928– )
- Norton (Winfred) Simon Biography (1907–93)
- Norway
- Norway Spruce
- Norwegian Literature
- Norwegian Sea
- Norwich (UK)
- Norwich (USA)
- Norwich School
- Nose
- Nostradamus Biography (1503–66) (Latin name of Michel de Notredame)
- Note-cluster
- Notebook
- Nothosaur
- Notochord
- Notre Dame (de Paris)
- Nottingham (Anglo-Saxon Snotingaham or Notingeham)
- Nottinghamshire
- Notungulata
- Nouadhibou (Fr Port Etienne)
- Nouakchott
- Noucentisme (Span novecentismo)
- Nouméa (formerly Port de France)
- Noureddine Morceli Biography (1970– )
- Nouvelle Cuisine
- Nova
- Nova Scotia
- Novalis Biography (1772–1801) (pseudonym of Friedrich Leopold von Hardenberg)
- Novatian Biography (3rd-c)
- Novaya Zemlya
- Novel
- Novel Proteins
- Novella ((Ital ‘tale’‘news’))
- Novemberrevolution
- Novgorod
- Novi Sad (Ger Neusatz)
- Novocaine
- Novosibirsk (formerly Novonikolaevsk (1903–25))
- Noël Coypel Biography (1628–1707)
- NTSC
- Nubian Desert
- Nubian Monuments
- Nuclear Disarmament
- Nuclear Fission
- Nuclear Fusion
- Nuclear Magnetic Resonance (NMR)
- Nuclear Physics
- Nuclear Proliferation
- Nuclear Reactor
- Nuclear Structure
- Nuclear Test-Ban Treaty
- Nuclear Weapons
- Nucleic Acids
- Nucleolus
- Nucleon
- Nucleon Number
- Nucleonics
- Nucleophile
- Nucleosome
- Nucleosynthesis
- Nucleotide
- Nucleus (astronomy)
- Nucleus (biology)
- Nucleus (physics)
- Nuclide
- Nueva Biblioteca De Autores Españoles (NBAE)
- Nueva Esparta
- Nuffield Radio Astronomy Laboratories
- Nuisance
- Nuku'alofa
- Nullarbor Plain
- Nullification
- Numa Pompilius Biography (c.700 BC)
- Numancia
- Numbat
- Number Line
- Number Theory
- Numbers
- Numbers, Book Of
- Numeral
- Numerical Analysis
- Numerical Control
- Numerology
- Numidia
- Numismatics
- Nummulites
- Nun
- Nunavut ((Inuktitut‘Our land’))
- Nunnally Johnson Biography (1897–1977)
- Nuno Gonçalves Biography (fl.1450–72)
- Nuremberg (Ger Nürnberg)
- Nuremberg Laws (Ger Nürnberger Gesetze)
- Nuremberg Trials
- Nuria Espert Biography (1935– )
- Nurse Shark
- Nursery Rhymes
- Nursery School
- Nursing
- Nut
- Nutation
- Nutcracker
- Nuthatch
- Nutmeg
- Nutrients
- Nutrition
- Nutritional Medicine
- Nutritional Minerals
- Nuzi
- Nuée Ardente ((‘burning cloud’))
- Nyala
- Nyasa (or MalawiLakeMozambique Niassa)
- Nylon
- Nymph (entomology)
- Nymph (mythology)
- Nymphalid Butterfly
- Nymphenburg Porcelain
- Nyons
- Nyoro
- Nîmes (ancient Nismes or Nemausus)
- Nördliche Kalkalpen
- O Henry Biography (1862–1910) (pseudonym of William Sydney Porteralso as Oliver HenryS H Peters)
- O Max Gardner Biography (1882–1947) (popular name of Oliver Maxwell Gardner)
- O(le) E(dvart) Rölvaag Or Roelvaag Biography (1876–1931) (pseudonym Paal Moerck)
- O(renthal) J(ames) Simpson Biography (1947– )
- O(sborn) B Hardison Biography (1928–90)
- O(scar) Glenn Stahl Biography (1910– )
- O(thniel) C(harles) Marsh Biography (1831–99)
- Oahu
- Oak
- Oak Ridge
- Oakes (botany) Ames Biography (1874–1950)
- Oakes (politics) Ames Biography (1804–73)
- Oakland
- Oarfish
- OAS (Algeria)
- Oasis
- Oath
- Oats
- Ob, River
- Obadiah (also called Abdias)
- Obadiah, Book Of
- Obed Hussey Biography (1792–1860)
- Obelisk
- Oberammergau Passion Play
- Oberon (astronomy)
- Oberon (mythology)
- Oberpfälzer Wald
- Obertenghi
- Oberösterreich
- Obesity
- Object-oriented Paradigm
- Objective Test
- Obliquity Of The Ecliptic
- Obo
- Oboe
- Observatory
- Obstetrics
- Ocarina
- Occasionalism
- Occluded Front
- Occultation
- Occultism
- Occupational Diseases
- Occupational Psychology
- Occupational Therapy
- Ocean
- Ocean Thermal Energy Conversion (OTEC)
- Oceania (also Oceanica)
- Oceanic Ridges
- Oceanic Trenches
- Oceanic Zone
- Oceanides
- Oceanography
- Oceanus
- Ocelot
- Ochre
- Octane Number
- Octans ((Lat ‘octant’))
- Octava (Eng ‘eight-line stanza')
- Octave (-Henri-Marie) Mirbeau Biography (1850–1917)
- Octave Chanute Biography (1832–1910)
- Octave Feuillet Biography (1821–90)
- Octavia Biography (c.69 BC–11 BC)
- Octavia Hill Biography (1838–1912)
- Octavien De Saint-Gelais Biography (1466–1502)
- Octavio Paz Biography (1914–98)
- Octavius Brooks Frothingham Biography (1822–95)
- Octet
- October Revolution
- Octopus
- Octopush
- Oda (Greek ‘a song accompanied by the lyre’)
- Oda Nobunaga Biography (1534–82)
- Odd Hassel Biography (1897–1981)
- Ode ((Gr ‘song’))
- Odense
- Oder, River (CzechPolish Odraancient Viadua)
- Oder–Neisse Line
- Odessa
- Odetta Biography (1930– ) (in full Odetta Holmes Felious Gordon)
- Odette Biography (1912–95) (popular name of Odette Hallowesformerly Churchill (to 1955) and Sansom (to 1946)née Brailly)
- Odilon Redon Biography (1840–1916)
- Odin
- Odissi
- Odo Biography (c.1036–97)
- Odoacer Biography (?–493) (also found as Odovacar)
- Odysseus
- Odysseus Elytis Biography (1911–96) (pseudonym of Odysseus Alepoudhelis)
- Oedema / Edema
- Oedipus
- Oedipus Complex
- Oesophagus / Esophagus
- Oestrogens / Estrogens
- Oestrus / Estrus
- Offa Biography (?–796)
- Offa's Dyke
- Offal
- Offaly (Ir Ua bhFailghe)
- Offenbach (am Main)
- Office Automation
- Office Of Fair Trading (OFT)
- Office Of Management And Budget (OMB)
- Office, Divine (or Holy)
- Ogaden
- Ogam Or Ogham
- Ogbomosho
- Ogden
- Ogden Codman Biography (1863–1951)
- Ogden Nicholas Rood Biography (1831–1902)
- Ogdensburg Agreement
- Ohio
- Ohio Company (1749)
- Ohio Company (1786)
- Ohio River
- Ohm
- Ohm's Law
- Ohmmeter
- Ohrid
- Ohrid, Lake (Serbo-Croatian Ohridsko Jezero)
- Oil (botany)
- Oil (earth Sciences)
- Oil Beetle
- Oil Painting
- Oil Palm
- Oil Pollution
- Oil Rig
- Oilbird
- Oireachtas
- Ojibwa
- Ojos Del Salado, Cerro
- Oka
- Okapi
- Okavango, River
- Okayama
- Okeechobee, Lake
- Okefenokee Swamp ((Muskogean ‘water-shaking’))
- Okhotsk, Sea Of (Russ Okhotskoye More)
- Okinawa
- Okinoshima
- Oklahoma ((Muskogean ‘red people’))
- Oklahoma City
- Okra
- Oktroyierte Verfassung
- Olaf I Tryggvason Biography (c.965–c.1000)
- Olaf II Haraldsson Biography (c.995–1030) (also called St Olaf)
- Olaf III Haraldsson Biography (?–1093)
- Olara (A) Otunnu Biography (1950– )
- Olaus (Johann) Murie Biography (1889–1963)
- Olav Duun Biography (1876–1939)
- Olav V Biography (1903–91)
- Olbers' Paradox
- Old Bailey
- Old Believers
- Old Catholics
- Old Comedy
- Old English
- Old English Sheepdog
- Old Testament
- Old Vic Theatre
- Old World Monkey
- Oldenburg
- Olduvai Gorge
- Ole (Christensen) Rømer Biography (1644–1710)
- Oleander
- Oleaster
- Oleg Cassini Biography (1913–2006)
- Oleg Grabar Biography (1929– )
- Oleg Konstantinovich Antonov Biography (1906–84)
- Olga Korbut Biography (1955– )
- Oligarchy
- Oligocene Epoch
- Oligomer
- Oligopoly
- Olin (Levi) Warner Biography (1844–96)
- Olindo Guerrini Biography (1845–1916) (pseudonym Lorenzo Stecchetti)
- Olingo
- Olive
- Olive (Emilie Albertina) Schreiner Biography (1855–1920) (pseudonym Ralph Iron)
- Olive Shell
- Oliver (Edwin) Baker Biography (1883–1949)
- Oliver (Fisher) Winchester Biography (1810–80)
- Oliver (Hazard Perry) La Farge Biography (1901–63)
- Oliver (Hazard) Perry (Throck) Morton Biography (1823–77)
- Oliver (Lemuel) Smith Biography (1918–94)
- Oliver (Wolf) Sacks Biography (1933– )
- Oliver Cromwell Biography (1599–1658)
- Oliver Ditson Biography (1811–88)
- Oliver Ellsworth Biography (1745–1807)
- Oliver Evans Biography (1755–1819)
- Oliver Goldsmith Biography (1728–74)
- Oliver Hazard Perry Biography (1785–1819)
- Oliver Heaviside Biography (1850–1925)
- Oliver Hudson Kelley Biography (1826–1913)
- Oliver Kahn Biography (1969– )
- Oliver Kirby Bovard Biography (1872–1945)
- Oliver North Biography (1943– )
- Oliver Otis Howard Biography (1830–1909)
- Oliver P Echols Biography (1892–1954)
- Oliver Stone Biography (1946– )
- Oliver Tambo Biography (1917–93)
- Oliver Wendell Holmes Biography (1809–94)
- Oliver Wolcott Biography (1760–1833)
- Olives, Mount Of Or Mount Olivet
- Olivia (Mary) De Havilland Biography (1916– )
- Olivia (Mary) Manning Biography (1908–80)
- Olivier (Eugène Prosper Charles) Messiaen Biography (1908–92)
- Olivier De La Marche Biography (1425–1502)
- Olivier Panis Biography (1966– )
- Olivine
- Olm
- Olmecs
- Olmützer Punktuation
- Olof Rudbeck Biography (1630–1702)
- Olof Von Dalin Biography (1708–63)
- Olympia (Greece) (Gr Olímbia)
- Olympia (USA)
- Olympia Brown Biography (1835–1926)
- Olympia Morata Biography (1526–55)
- Olympians
- Olympias Biography (c.375–316 BC)
- Olympic Games
- Olympic National Park
- Olympus Mons
- Olympus, Mount (Cyprus)
- Olympus, Mount (Greece) (Gr Olimbos)
- Olynthus
- Oléron, Ile D'
- Om
- Omagh (Ir An Omaigh)
- Omaha (Indians)
- Omaha (Nebraska)
- Oman (formerly Muscat and Oman)
- Oman, Gulf Of
- Omar (Nelson) Bradley Biography (1893–1981)
- Omar Bongo Biography (1935– ) (originally Albert-Bernard Bongo)
- Omar Khayyám Biography (c.1050–c.1122) (also spelled Umar Khayyám)
- Omar Or Umar I Biography (c.581–644)
- Omar Sharif Biography (1932– ) (originally Michael Shalhouz)
- Ombudsman ((Swed ‘agent’ or ‘representative’))
- Omdurman
- Omdurman, Battle Of
- Ommelanden
- Omnivore
- Omo
- Omri Biography (9th-c BC)
- Omsk
- On-line Processing
- Oncogene
- Oncology
- Ondes Martenot
- Ondárroa
- One Nation
- Onega, Lake (Russ Ozero Onezhskoye)
- Oneglia
- Oneida
- Onesimus Biography (fl.1706–21)
- Onion
- Onomastics
- Onomatopoeia ((Gr ‘name-making’))
- Onsen
- Ontario
- Ontario, Lake
- Ontological Argument
- Ontology
- Onychophora
- Oodgeroo Noonuccal Biography (1920–93) (originally Kath(leen Jean Mary) Walker)
- Oolite
- Oorschot, Van
- Oort Cloud
- Op Art
- Opal
- OPEC (Organization Of Petroleum Exporting Countries)
- Open Cluster
- Open Door
- Open Enrolment
- Open Golf Championship
- Open Government
- Open Plan
- Open Stage
- Open Systems Interconnection (OSI)
- Open Theater
- Open University
- Open-ended Investment Company
- Open-hearth Process
- Open-market Operations
- Open-plan School
- Opera
- Operant
- Operating System
- Operationalism
- Operetta
- Operon
- Ophir
- Ophiuchus ((Gr ‘serpent bearer’))
- Ophthalmia
- Ophthalmology
- Opinion Poll
- Opioid Peptides
- Opium
- Opium Poppy
- Opium Wars
- Oporto
- Opossum
- Opposition (astronomy)
- Opposition (politics)
- Oprah (Gail) Winfrey Biography (1954– )
- Ops
- Optical Activity
- Optical Character Reader (OCR)
- Optical Fibres
- Optical Sensing
- Optics
- Optimum Currency Area
- Options Market
- Optoelectronics
- Optometry
- Opuntia
- Opus Dei ((Lat ‘work of God’))
- Or Ibrahiz Abraham, Abram Biography (after 2000 BC)
- Or P'u-i Puyi, Pu Yi Biography (1906–67) (personal name of the Xuantong Emperor)
- Orache
- Oracle
- Oracle (computing)
- Oracle (telecommunications)
- Oracle Bones
- Oracy
- Oral History
- Oran (or Wahran)
- Oran Page Biography (1908–54) (known as Hot Lips)
- Orang-utan
- Orange
- Orange (France)
- Orange (Massachusetts)
- Orange (New Jersey)
- Orange Order
- Orange Prize
- Orange River (Afrikaans Oranjerivier)
- Orange, Huis Van
- Oratorians
- Oratorio
- Oratory
- Orazio Gentileschi Biography (1562–1647)
- Orb Weaver
- Orbit
- Orcagna Biography (c.1308–c.1368) (originally Andrea de Cione)
- Orchestra
- Orchestration
- Orchid
- Orde (Charles) Wingate Biography (1903–44)
- Ordelaffi
- Order In Council
- Order Of Merit (OM)
- Order Of Reaction
- Ordered Pairs
- Orders Of Architecture
- Orders, Holy
- Ordinance Of 1787
- Ordnance Datum (OD)
- Ordnance Survey Of Great Britain
- Ordovician Period
- Ore
- Oregon
- Oregon Boundary Dispute
- Oregon Grape
- Oregon Trail
- Orel
- Oreste Baratieri Biography (1841–1901)
- Oreste Del Buono Biography (1923– )
- Orestes
- Orestes (Augustus) Brownson Biography (1803–76)
- Orfe
- Organ
- Organic Architecture
- Organic Chemistry
- Organic Farming
- Organization For Economic Co-operation And Development (OECD)
- Organization For European Economic Co-operation (OEEC)
- Organization For Security And Co-operation In Europe (OSCE) (formerly known as Conference on Security and Co-operation in Europe (CSCE))
- Organization Of American States (OAS)
- Organization Of Arab Petroleum Exporting Countries (OAPEC)
- Organization Of Central American States
- Organization Of The Islamic Conference
- Organum
- Orgone Therapy
- Orhan Pamuk Biography (1952– )
- Orhon Gol, River
- Oriana Fallaci Biography (1929–2006)
- Oribi
- Orienteering
- Origami
- Origen Biography (c.185–c.254)
- Original Dixieland Jazz Band
- Original Sin
- Oriol Bohigas I Guardiola Biography (1925– )
- Oriole
- Orion (astronomy)
- Orion (mythology)
- Orissa
- Orkney
- Orland R Sweeney Biography (1883–1958)
- Orlando
- Orlando Bloom Biography (1977– )
- Orlando Gibbons Biography (1583–1625)
- Orlando W Wilson Biography (1900–72)
- Orlandus Lassus Biography (c.1532–94) (also known as Orlando di Lasso)
- Orleans (Fr Orléansancient Aurelianum)
- Orléans, House Of
- Orm Biography (fl.c.1200)
- Ormolu Or Ormulu
- Ornette Coleman Biography (1930– )
- Ornithischia
- Ornithology
- Orogeny
- Orographic Rain
- Oromo
- Orpheus
- Orphism
- Orris
- Orris Sanford Ferry Biography (1823–75)
- Orseolo
- Orsini
- Ortelius Biography (1527–98) (Latin name of Abraham Ortels)
- Orthicon
- Orthoclase
- Orthodox Church Or Eastern Orthodox Church
- Orthographic Projection
- Orthopaedics / Orthopedics
- Orthoptera
- Ortolan
- Orust
- Orville E Babcock Biography (1835–84)
- Orycteropodidae
- Oryx
- Osaka (formerly Naniwa)
- Osama Bin Laden Biography (1955–?)
- Osami Nagano Biography (1880–1947)
- Osbert Guy Stanhope Crawford Biography (1886–1957)
- Osborne Reynolds Biography (1842–1912)
- Oscans
- Oscar
- Oscar (Arnulfo) Romero (y Galdames) Biography (1917–80)
- Oscar (Emmanuel) Peterson Biography (1925– )
- Oscar (Fingal O'Flahertie Wills) Wilde Biography (1854–1900)
- Oscar (Luigi) Scalfaro Biography (1918– )
- Oscar (Theodore) Broneer Biography (1894–1992)
- Oscar (Wilder) Underwood Biography (1862–1929)
- Oscar Bluemner Biography (1867–1938)
- Oscar Cullman Biography (1902–99)
- Oscar De La Renta Biography (1932– )
- Oscar Edward Meinzer Biography (1876–1948)
- Oscar Hammerstein Biography (1846–1919)
- Oscar Handlin Biography (1915– )
- Oscar Howe Biography (1915–83)
- Oscar Levant Biography (1906–72)
- Oscar Lewis Biography (1914–70)
- Oscar Micheaux Biography (1884–1951)
- Oscar Niemeyer Biography (1907– )
- Oscar Robertson Biography (1938– ) (nickname the Big O)
- Oscar Solomon Straus Biography (1850–1926)
- Oscar Stanton De Priest Biography (1871–1951)
- Oscar Straus Biography (1870–1954)
- Oscar Thompson Biography (1887–1945)
- Oscar Zariski Biography (1899–1986)
- Oscar-Vladislas De Lubisez Milosz Biography (1877–1939)
- Osceola Biography (c.1800–38) (also known as Powell)
- Oscillation
- Oscillator
- Osier
- Osimo, Treaty Of
- Osip Emilevich Mandelstam Biography (1891–1938)
- Osiris
- Osius Biography (256–357)
- Oskar (Johann Viktor) Anderson Biography (1887–1960)
- Oskar Kokoschka Biography (1886–1980)
- Oskar Lafontaine Biography (1943– ) (nicknames Red Oskar and Ayatollah of the Saarland)
- Oskar Loerke Biography (1884–1941)
- Oskar Maria Graf Biography (1894–1967) (originally Oskar G Berg)
- Oskar Morganstern Biography (1902–77)
- Oskar Schlemmer Biography (1888–1943)
- Oslo (formerly Christiania or Kristiania)
- Osman I Biography (1258–1324)
- Osmiridium
- Osmotic Pressure
- Osnabrück
- Osprey
- Ossa, Mount
- Ossian Cole Simonds Biography (1855–1926)
- Ossian Or Oisín
- Ossie Davis Biography (1917–2005)
- Ossip (Solomonovitch) Gabrilowitsch Biography (1878–1936)
- Ossip Zadkine Biography (1890–1967)
- Ossola, Republic Of
- Ossory
- Ostend (Flemish OostendeFr Ostende)
- Osteoarthritis
- Osteology
- Osteomalacia
- Osteomyelitis
- Osteopathy
- Osteoporosis
- Ostermarsch
- Ostia
- Ostracism
- Ostracod
- Ostrava
- Ostrich
- Ostrogoths
- Ostsiedlung (also known as Ostkolonisation)
- Oswald Achenbach Biography (1827–1905)
- Oswald Garrison Villard Biography (1872–1949)
- Oswald Mbuyiseni Mtshali Biography (1940– )
- Oswald Spengler Biography (1880–1936)
- Oswald T(heodore) Avery Biography (1877–1955)
- Oswald Veblen Biography (1880–1960)
- Oswald Von Wolkenstein Biography (c.1337–1445)
- Otfried Preußler Biography (1923– )
- Othmar Hermann Ammann Biography (1879–1965)
- Otis Chandler Biography (1927–2006)
- Otis D(udley) Duncan Biography (1921–2004)
- Otis Redding Biography (1941–67)
- Otis Rush Biography (1934– )
- Otis Skinner Biography (1858–1942)
- Otl Aicher Biography (1922–91) (known as Otto)
- Otmar Alt Biography (1940– )
- Ottavio Missoni Biography (1921– ) (known as Tai Ottavio)
- Ottawa
- Ottawa Agreements
- Ottawa River (Fr Rivière des Outaouais)
- Otter
- Otter Hound
- Otter Shrew
- Ottiero Ottieri Biography (1924– )
- Ottmar Merganthaler Biography (1854–99)
- Ottmar Mergenthaler Biography (1854–99)
- Otto (Alfred) Piper Biography (1891–1982)
- Otto (Heinrich) Warburg Biography (1883–1970)
- Otto (Herman) Kahn Biography (1867–1934)
- Otto (Knut Olof) Folin Biography (1867–1934)
- Otto Behaghel Biography (1854–1936)
- Otto Braun Biography (1872–1955)
- Otto Diels Biography (1876–1954)
- Otto Dietrich Biography (1897–1952)
- Otto Dix Biography (1891–1969)
- Otto Eckstein Biography (1927–84)
- Otto Erich Hartleben Biography (1865–1905) (pseudonym Otto Erich)
- Otto F Walter Biography (1928–94)
- Otto Fritz Meyerhof Biography (1884–1951)
- Otto Georg Thierack Biography (1889–1946)
- Otto Geßler Biography (1875–1955)
- Otto Grotewohl Biography (1894–1964)
- Otto Hahn Biography (1879–1968)
- Otto Harbach Biography (1873–1963) (originally Otto Abels Hauerbach)
- Otto I Biography (912–73) (known as the Great)
- Otto II Biography (955–83)
- Otto III Biography (980–1002)
- Otto IV Of Brunswick Biography (d.1218)
- Otto John Biography (1909–97)
- Otto Julius Bierbaum Biography (1865–1910) (pseudonym Martin Möbius)
- Otto Klemperer Biography (1885–1973)
- Otto Kotzebue Biography (1787–1846)
- Otto Laporte Biography (1902–71)
- Otto Lilienthal Biography (1849–96)
- Otto Loewi Biography (1873–1961)
- Otto Ludwig Biography (1813–65)
- Otto Messmer Biography (1894–1985)
- Otto Natzler Biography (1908– )
- Otto Neugebauer Biography (1899–1990)
- Otto Neurath Biography (1882–1945)
- Otto Preminger Biography (1906–86)
- Otto Robert Frisch Biography (1904–79)
- Otto Skorzeny Biography (1908–75)
- Otto Stern Biography (1888–1969)
- Otto Struve Biography (1897–1963)
- Otto Van Veen Biography (c.1556–1634)
- Otto Von Guericke Biography (1602–86)
- Otto Wagner Biography (1841–1918)
- Otto Wilhelm Struve Biography (1819–1905)
- Ottoman Empire
- Ottomar Anschütz Biography (1846–1907)
- Ottonen
- Ottonian Art
- Ottorino Respighi Biography (1879–1936)
- Ouagadougou
- Oudenaarde (Fr Audenarde)
- Ouida Biography (1839–1908) (pseudonym of Marie Louise de la Ramée)
- Ouija Board
- Oujda
- Oulipo (in full Ouvroir de Littérature Potentielle)
- Oulu (Swed Uleåborg)
- Ouray Biography (?1820/1833–80)
- Ourense
- Ouro Prêto (formerly Vila Rica)
- Ouse, River (C England)
- Ouse, River (E England)
- Ouse, River (NE England)
- Ouse, River (S England)
- Out-of-the-body Experience (OOBE Or OBE)
- Ouzel Or Ousel
- Ouzo
- Oval, The
- Ovamboland
- Ovarian Follicle
- Ovary
- Over-the-counter (OTC) Trading
- Over-the-counter Drugs (OTCs)
- Overijssel
- Overland Telegraph
- Overpopulation
- Overture
- Oveta Culp Hobby Biography (1905–95)
- Ovid Biography (43 BC–AD 17) (in full Publius Ovidius Naso)
- Ovide Mercredi Biography (1946– )
- Oviedo
- Ovillejo
- Ovimbundu
- Ovule
- Owain Arwel Hughes Biography (1942– )
- Owen Chamberlain Biography (1920–2006)
- Owen D Young Biography (1874–1962)
- Owen Davis Biography (1874–1956)
- Owen Glendower Biography (c.1354–c.1416) (Welsh Owain Glyndwr or Owain ap Gruffudd)
- Owen J(osephus) Roberts Biography (1875–1955)
- Owen Jones Biography (1809–74)
- Owen Lattimore Biography (1900–89)
- Owen Lovejoy Biography (1811–64)
- Owen Wister Biography (1860–1938)
- Owl
- Owlet Frogmouth
- Ox
- Ox-eye Daisy
- Oxalic Acid
- Oxalis
- OXFAM
- Oxford (UK) (Lat Oxonia)
- Oxford (USA)
- Oxford Movement
- Oxford University
- Oxford, Provisions Of
- Oxfordshire
- Oxidation
- Oxides
- Oxidizing Agent
- Oxlip
- Oxpecker
- Oxyacetylene Welding
- Oxygen
- Oxygen Cycle
- Oxytocin
- Oystein Ore Biography (1899–1968)
- Oyster
- Oystercatcher
- Ozark Mountains ((Fr aux arks‘at the arks’))
- Ozone
- Ozone Layer
- Ozzie Osbourne Biography (1948– ) (popular name of John Michael Osbourne)
- Ozzie Smith Biography (1954– ) (popular name of Osborne Earl Smithnickname the Wizard of Oz)
- P D James Biography (1920– ) (pseudonym of Phyllis Dorothy WhiteBaroness James of Holland Park)
- P F Thomése Biography (1958– )
- P José Antonio De Donostia Biography (1886–1956) (originally José Gonzalo Zulaica Arregui)
- P(amela) L(yndon) Travers Biography (1906–96) (originally Helen Lyndon Goff)
- P(atrick) J(ohn) Kenedy Biography (1843–1906)
- P(ercival) C(hristopher) Wren Biography (1875–1941)
- P(hilip) D(ey) Eastman Biography (1909–86)
- P(hineas) T(aylor) Barnum Biography (1810–91)
- P(ieter) W(illem) Botha Biography (1916–2006)
- P(indaros) Roy Vagelos Biography (1929– )
- P2
- Paavo (Johannes) Nurmi Biography (1897–1973)
- Paavo (Tapio) Lipponen Biography (1941– )
- Pablo (Martin Melitón) Sarasate (y Navascué) Biography (1844–1908)
- Pablo Bertrán Y Bros Biography (1853–91)
- Pablo Casals Biography (1876–1973) (Catalan Pau)
- Pablo De Céspedes Biography (1538–1608)
- Pablo García De Santa María Biography (1350–1435)
- Pablo Neruda Biography (1904–73) (pseudonym of Neftali Ricardo Reyes y Basualto)
- Pablo Picasso Biography (1881–1973)
- Paca
- Pacarana
- Pacemaker
- Pachinko
- Pachtersoproer
- Pachyderm
- Pacific Community (formerly South Pacific Commission (to 1997))
- Pacific Ocean
- Pacific Scandal
- Pacifism
- Pacifistisch-Socialistische Partij (PSP)
- Pack Rat
- Packet Switching
- Padang
- Padania
- Paddle Tennis
- Paddlefish
- Paddy Ashdown Biography (1941– ) (popular name of Lord Jeremy John Durham Ashdown of Norton-sub-Hamdon)
- Paddy Chayefsky Biography (1923–81) (originally Sidney Chayefsky)
- Padraic Colum Biography (1881–1972)
- Padua (Ital Padovaancient Patavium)
- Paediatrics / Pediatrics
- Paedophilia / Pedophilia
- Paestum
- Pafnuty Lvovich Chebyshev Biography (1821–94)
- PageMaker®
- Pager
- Paget's Disease
- Pagoda
- Pahang
- Pahang, River
- Pahari
- Paharpur Vihara
- Pain
- Paint
- Painted Lady
- Painting
- Pair Production
- Paisley
- Paiute
- Pakistan
- PAL
- Pala
- Palaeocene / Paleocene Epoch
- Palaeoclimatology / Paleoclimatology
- Palaeoecology / Paleoecology
- Palaeogeography / Paleogeography
- Palaeography / Paleography
- Palaeolithic / Paleolithic
- Palaeolithic / Paleolithic Art
- Palaeomagnetism / Paleomagnetism
- Palaeontology / Paleontology
- Palaeopathology / Paleopathology
- Palaeozoic / Paleozoic Era
- Palaeozoology / Paleozoology
- Palafitte
- Palais Omnisports Paris-Bercy
- Palantype
- Palate
- Palatinate, The
- Palau De La Música Catalana (Eng Catalan Palace of Music)
- Palawan (formerly Paragua (1902–5))
- Pale
- Palembang
- Palencia
- Palenque
- Palermo
- Palestine (Middle East)
- Palestine (USA)
- Palestine National Authority (PNA)
- Palette
- Palindrome
- Palingoproer
- Palio
- Palladianism
- Palladium
- Pallas
- Pallas's Cat
- Pallavicino
- Pallium Or Pall
- Palm
- Palm Oil
- Palm Springs
- Palm Sunday
- Palma (de Mallorca)
- Palma, La
- Palmate
- Palmerston North
- Palmiro Togliatti Biography (1893–1964)
- Palmitic Acid
- Palmyra (Pacific Ocean)
- Palmyra (Roman History)
- Palo Alto
- Palomar Observatory
- Palomino
- Palynology
- Pam Gems Biography (1925– ) (popular name of Iris Pamela Gemsnée Price)
- Pamela Frankau Biography (1908–67) (pseudonym Eliot Naylor)
- Pamela Hansford Johnson Biography (1912–81)
- Pampa(s)
- Pampas Cat
- Pampas Grass
- Pamplona (Lat Pampeluna or Pompaelo)
- Pamporovo
- Pan (astronomy)
- Pan (mythology)
- Pan-Africanism
- Pan-Africanist Congress
- Pan-American Games
- Pan-American Highway
- Pan-American Union
- Pan-and-scan
- Panaetius Biography (c.185–c.110 BC)
- Panama
- Panama Canal
- Panama City (Span Panamá)
- Panathenaea
- Panchen Lama
- Pancho Gonzales Biography (1928–95) (popular name of Ricardo Alonzo Gonzales)
- Pancho Villa Biography (1878–1923) (also known as Francisco Villaoriginally Doroteo Arango)
- Pancreas
- Panda
- Pandarus
- Pandora
- Pandurang Shastri Athavale Biography (1920– )
- Panegyric
- Pangaea
- Pangamic Acid
- Pangolin
- Pangram
- Pangu Or P'an-ku
- Panhandle
- Panicle
- Paninari
- Panini Biography (5th–7th-c BC)
- Panorama
- Panoramic Camera
- Panos Demetrios Callimachos Biography (1879–1963) (originally Demetrios Paximadas)
- Panpipes
- Pansy
- Pantheism
- Pantheon
- Panther
- Pantomime
- Pantonality
- Pantothenic Acid
- Panzer ((Ger ‘armour’))
- Paolo Emilio Imbriani Biography (1808–77)
- Paolo Ferrari Biography (1822–89)
- Paolo Maldini Biography (1968– )
- Paolo Monelli Biography (1894–1984)
- Paolo Savi Biography (1798–1871)
- Paolo Uccello Biography (1397–1475) (originally Paolo di Dono)
- Paolo Veronese Biography (c.1528–88) (originally Paolo Caliari)
- Paolo Volponi Biography (1924–94)
- Papago
- Papakura
- Papal States
- Papaw
- Papeete
- Paper
- Paper Nautilus
- Paper-bark Birch
- Paphos
- Papilionid Butterfly
- Papilloma
- Papillon
- Pappus Of Alexandria Biography (4th-c)
- Pappy Boyington Biography (1912–88) (popular name of Gregory Boyington)
- Papua New Guinea
- Papyrus
- Paquita Rico Biography (1929– ) (originally Francisca Rico Martínez)
- Parable
- Parabola
- Paracas
- Paracelsus Biography (1493–1541) (originally Philippus Aureolus Theophrastus Bombastus von Hohenheim)
- Paracetamol
- Parachuting
- Paracrine
- Paradise
- Paradox
- Paraffin Wax
- Paraguay
- Paraguay, River ((Span Río)Port Rio Paraguai)
- Parakeet
- Paraldehyde
- Parallax
- Parallel Processing
- Paralympics ((an abbreviation of ‘Parallel Olympics’))
- Paralysis
- Paramagnetic Resonance
- Paramagnetism
- Paramaribo
- Paramedic