complement

noun

• 1a 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

• 2 [in singular] a number or quantity of something, especially that required to make a group complete:at the moment we have a full complement of staff
• the number of people required to crew a ship:almost half the ship’s complement of 322 were wounded
• Geometry the amount in degrees by which a given angle is less than 90°.
• Mathematics the members of a set or class that are not members of a given subset.

• 3 Grammar 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.
• (in systemic grammar) an adjective or noun that has the same reference as either the subject (as mad in he is mad) or the object (as mad in he drove her mad or manager in they appointed him manager).

• 4 [mass noun] Physiology 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.

verb

• 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
• add to or make complete:the proposals complement the incentives already available