noun

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

accompaniment,companion,addition,supplement,accessory,adjunct,trimming,finishing touch,final touch

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

accompany,go with,round off,set off,suit,harmonize with,be the perfect companion to,be the perfect addition to,add the finishing touch to,add the final touch to,add to,supplement,augment,enhance,complete