1.  To supply a lack; to supplement. [1913 Webster]

2.  To compliment. Jer. Taylor. [1913 Webster]

complement, n. & v.
--n.
1 a something that completes. b one of a pair, or one of two things that go together.
2 (often full complement) the full number needed to man a ship, fill a conveyance, etc.
3 Gram. a word or phrase added to a verb to complete the predicate of a sentence.
4 Biochem. a group of proteins in the blood capable of lysing bacteria etc.
5 Math. any element not belonging to a specified set or class.
6 Geom. the amount by which an angle is less than 90° (cf. SUPPLEMENT).
--v.tr.
1 complete.
2 form a complement to (the scarf complements her dress).

Derivative:
complemental adj.

Etymology:
ME f. L complementum (as COMPLETE)

N  adjunct, addition, additament, additum, affix, appelidage, annexe, annex, augment, augmentation, increment, reinforcement, supernumerary, accessory, item, garnish, sauce, accompaniment, adjective, addendum, complement, supplement, continuation, rider, offshoot, episode, side issue, corollary, piece, flap, lappet, skirt, embroidery, trappings, cortege, tail, suffix, wing, additional, alate, alated, winged, in addition.

N  remainder, residue, remains, remanent, remnant, rest, relic, leavings, heeltap, odds and ends, cheesepairings, candle ends, orts, residuum, dregs, refuse, stubble, result, educt, fag-end, ruins, wreck, skeleton, stump, alluvium, surplus, overplus, excess, balance, complement, superplus, surplusage, superfluity, survival, survivance, remaining, left, left behind left over, residual, residuary, over, odd, unconsumed, sedimentary, surviving, net, exceeding, over and above, outlying, outstanding, cast off, superfluous.

N  completeness, completion, integration, allness, entirety, perfection, solidity, solidarity, unity, all, ne plus ultra, ideal, limit, complement, supplement, make-weight, filling, up, impletion, saturation, saturity, high water, high tide, flood tide, spring tide, fill, load, bumper, bellyful, brimmer, sufficiency, complete, entire, whole, perfect, full, good, absolute, thorough, plenary, solid, undivided, with all its parts, all- sided, exhaustive, radical, sweeping, thorough-going, dead, regular, consummate, unmitigated, sheer, unqualified, unconditional, free, abundant, brimming, brimful, topful, topfull, chock full, choke full, as full as an egg is of meat, as full as a vetch, saturated, crammed, replete, fraught, laden, full-laden, full-fraught, full-charged, heavy laden, completing, supplemental, supplementary, ascititious, completely, altogether, outright, wholly, totally, in toto, quite, all out, over head and ears, effectually, for good and all, nicely, fully, through thick and thin, head and shoulders, neck and heel, neck and crop, in all respects, in every respect, at all points, out and out, to all intents and purposes, toto coelo, utterly, clean, clean as a whistle, to the full, to the utmost, to the backbone, hollow, stark, heart and soul, root and branch, down to the ground, to the top of one's bent, as far as possible, a outrance, throughout, from first to last, from beginning to end, from end to end, from one end to the other, from Dan to Beersheba, from head to foot, from top to toe, from top to bottom, de fond en comble, a fond, a capite ad calcem, ab ovo usque ad mala, fore and aft, every, whit, every inch, cap-a-pie, to the end of the chapter, up to the brim, up to the ears, up to the eyes, as a as can be, on all accounts, sous tous les rapports, with a vengeance, with a witness, falsus in uno falsus in omnibus, false in one thing, false in everything, omnem movere lapidem, una scopa nuova spazza bene.

N  number, symbol, numeral, figure, cipher, digit, integer, counter, round number, formula, function, series, sum, difference, complement, subtrahend, product, multiplicand, multiplier, multiplicator, coefficient, multiple, dividend, divisor, factor, quotient, submultiple, fraction, rational number, surd, irrational number, transcendental number, mixed number, complex number, complex conjugate, numerator, denominator, decimal, circulating decimal, repetend, common measure, aliquot part, prime number, prime, relative prime, prime factor, prime pair, reciprocal, totient, binary number, octal number, hexadecimal number, permutation, combination, variation, election, ratio, proportion, comparison, progression, arithmetical progression, geometrical progression, harmonical progression, percentage, permilage, figurate numbers, pyramidal numbers, polygonal numbers, power, root, exponent, index, logarithm, antilogarithm, modulus, base, differential, integral, fluxion, fluent, numeral, complementary, divisible, aliquot, reciprocal, prime, relatively prime, fractional, decimal, figurate, incommensurable, proportional, exponential, logarithmic, logometric, differential, fluxional, integral, totitive, positive, negative, rational, irrational, surd, radical, real, complex, imaginary, finite, infinite, impossible, numerically, modulo.

complement fixation, complement fixation test, full complement