The words complement and compliment are sometimes confused because they look so similar. These words, however, have two distinctly different meanings.
Complement may be a verb or a noun.
As a verb, complement means to complete, to bring to perfection, to go well with.
As a noun, complement refers to the thing which gives completion or perfection.
Compliment may be a verb or a noun.
As a verb, compliment means to offer praise or flattery.
As a noun, compliment refers to the praise or flattery offered.
Link to exercises on complement / compliment..