Both words sound the same when pronounced, but their meanings are very different. Compliment means to give praise, express admiration or giving congratulations. Complement, on the other hand, means completing something or to make something perfect. A good way to always remember the difference is to remember that the word with the “e” means complete. In fact, the word complete is almost entirely spelled within complement.
Complement is used when what you are trying to convey that something is essentially made complete with something else. For example, if you were describing colors that look good together or a relationship involving two people who seem well matched, complement is the correct choice. Complement functions as both a noun and a verb.
Incorrect: The striped throw pillows complimented the sofa colors quite nicely. (This implies that the pillows gave praise to the sofa, which is impossible).
Correct: The colors in the pillows complemented the stripes in the sofa very well. (Complement is a verb in this sentence).
Compliment is used when you are aiming to offer praise. For example, you might compliment someone on a new hairdo or on an outfit that is particularly flattering. In its plural form it can mean you are offering multiple expressions of praise, or it can mean best wishes. Compliment functions as both a noun and a verb.
Incorrect: She paid her boss a complement about how well her hair highlights complement her complexion. (The first complement is incorrect because “her boss” does not complete anything, which is implied by spelling the word with an “e.”
Correct: She paid her boss a nice compliment on how well her new hairdo complemented her complexion. (Compliment is a noun in this sentence).
Complimentary is an adjective that is very similar to compliment, but it also has other meanings. It can mean that something contains or expresses compliments, that something is favorable or that something is free, as in a complimentary breakfast at a hotel.