COMPLEMENT (

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• LAT

Lat. complementum, from complere, to fill up)  , that which fills up or completes anything, e.g. the number of men necessary to man a ship . In geometry, the complement of an angle is the difference between the angle and a right angle; the complements of a parallelogram are formed by drawing parallel to adjacent sides of a parallelogram two lines intersecting on a diagonal; four parallelograms are thus formed, and the two not about the diagonal of the original parallelogram are the complements of the parallelogram . In analysis, a complementary function is a partial solution to a differential equation (q.v.); complementary operators are reciprocal or inverse operators, i.e. two operations A and B are complementary when both operating on the same figure or function leave it unchanged . A " complementary colour " is one which produces white when mixed with another (see CoLouR) . In Spanish the word cumplimento was used in a particular sense of the fulfilment of the duties of polite behaviour and courtesy, and it came through the French and Italian forms into use in English, with a change in spelling to " compliment," with the sense of an act of politeness, especially of a polite expression of praise, or of social regard andgreetings . The word " comply," meaning to act in accordance with wishes, orders or conditions, is also derived from the same origin, but in sense is connected with " ply " or " pliant," from Lat. plicare, to bend, with the idea of subserviently yielding to the wishes of another .