NIGHT  , that

part of the natural day of twenty-four hours during which the sun is below the horizon, the dark part of the day from sunset to sunrise (see DAY) . The word in O . Eng. takes two forms, neaht and night, the latter form apparently being established by about the loth century . The word is common in varying forms to Indo-European languages . The root is usually taken to be nak-, to perish, the word meaning the time when the light fails (cf . Gr . 4icos, Lat. nex, death, nocere, to hurt) . It was customary to reckon periods of time by nights, and we still use " fortnight " (O . Eng. feowertyne niht, fourteen nights), but " se'n-night " (seven nights) has been displaced by " week " (q.v.) .