a thing that contributes extra features to something else in such a way as to improve or emphasize its quality

local ales provide the perfect complement to fine food

a number or quantity of something, especially that required to make a group complete

at the moment we have a full complement of staff

one or more words, phrases, or clauses governed by a verb (or by a nominalization or a predicative adjective) that complete the meaning of the predicate. In generative grammar, all the constituents of a sentence that are governed by a verb form the complement

a group of proteins present in blood plasma and tissue fluid which combine with an antigen–antibody complex to bring about the lysis of foreign cells

contribute extra features to (someone or something) in such a way as to improve or emphasize their qualities

a classic blazer complements a look that's smart or casual