compliment vs. complement  

These two words have the same pronunciation—/ˈkɒmpləmənt/—but they have very different meanings. The more common of the two, compliment, is usually a noun meaning “a remark, expression, or gesture of respect, praise, commendation, or admiration.” It can also be used as a verb meaning “to make such a remark, expression, or gesture.” For example:

Complement, on the other hand, generally refers to something that completes, improves, or perfects something else. Like compliment, it can also function as a verb to describe the act of completing, improving, or perfecting something. For example:

(Complement also has a few other specific meanings that extend from this basic definition, such as “an angle related to another such that their sum is equal to 90°”; the quantity or amount that fills or completes something; and, in grammar, “a word or group of words necessary to complete the meaning of another part of a sentence.”)

Although compliment is the more common word, be careful not to use it in situations in which complement is the correct spelling. Remember, a complement completes something else, which is why it is spelled with an E.