adj. & n.
adj. 1 chief, most important (the prime agent; the prime motive). 2 (esp. of cattle and provisions) first-rate, excellent. 3 primary, fundamental. 4 Math. a (of a number) divisible only by itself and unity (e.g. 2, 3, 5, 7, 11). b (of numbers) having no common factor but unity.
n. 1 the state of the highest perfection of something (in the prime of life). 2 (prec. by the; foll. by of) the best part. 3 the beginning or first age of anything. 4 Eccl. a the second canonical hour of prayer, appointed for the first hour of the day (i.e. 6 a.m.). b the office of this. c archaic this time. 5 a prime number. 6 Printing a symbol (') added to a letter etc. as a distinguishing mark, or to a figure as a symbol for minutes or feet. 7 the first of eight parrying positions in fencing. prime cost the direct cost of a commodity in terms of materials, labour, etc. prime meridian 1 the meridian from which longitude is reckoned, esp. that passing through Greenwich. 2 the corresponding line on a map. prime minister the head of an elected government; the principal minister of a sovereign or State. prime mover 1 an initial natural or mechanical source of motive power. 2 the author of a fruitful idea. prime rate the lowest rate at which money can be borrowed commercially. prime time the time at which a radio or television audience is expected to be at its highest. prime vertical the great circle of the heavens passing through the zenith and the E. and W. points of the horizon. primeness n.
[ (n.) OE prim f. L prima (hora) first (hour), & MF f. OF prime: (adj.) ME f. OF f. L primus first ]