Real Dictionary

complement
a group or combination of interrelated, interdependent, or interacting elements forming a collective entity; a methodical or coordinated assemblage of parts, facts, concepts, etc [...]
a person or thing that completes something [...]
to make active or capable of action [...]
verb: If one thing complements another, it goes well with the other thing and makes its good qualities more noticeable.
verb: If people or things complement each other, they are different or do something different, which makes them a good combination.