They sound alike, and they’re different by only one letter, so it’s easy to confuse “compliment” and “complement.”
“Compliment” with an I is a noun and a verb referring to an expression of praise or admiration.
“Dr. Watson complimented Sherlock Holmes on his deductive reasoning skills. In return, Holmes paid Watson a compliment for his medical knowledge.”
“Complement” with an E is a verb that means go with, complete, enhance or work together well, and a noun referring to things (or people) that do so.
“Holmes and Watson work well together because their personalities complement each other. Watson’s steadiness is a complement to Holmes’ eccentricities.”
The adjective forms – “complimentary” and “complementary” are what trip most people up, especially when we’re talking about free stuff.
“Complimentary” with an I is the correct word to use when referring to tickets, drinks, meals or other things provided at no charge.
“For my birthday, I received a complimentary membership to the Sherlock Holmes Society. The coffee shop where we meet has complimentary Wi-Fi.”
Memory trick: Compliments are nice things to receive. So are freebies. When referring to either, use the word that shares a vowel with the word “nice.”