Complement. Complement is a noun and verb. It also has a matching adjective, complementary. In any case, it refers to something that completes or goes well with something. The sauce is a nice complement to the vegetables.The sauce complements the vegetables nicely.The sauce is nicely complementary to the vegetables.omplement is a noun and verb. It also has a matching adjective, complementary. In any case, it refers to something that completes or goes well with something. The sauce is a nice complement to the vegetables. The sauce complements the vegetables nicely. The sauce is nicely complementary to the vegetables.