With examples from Stargate SG-1 and Harry Potter
It is so easy to confuse these two words because they are homophones (words that sound alike, but have different spellings and meanings), and to confuse things even more, both words can be used as nouns and as verbs.
So what's the difference?
Dictionary.com states that compliment is "an expression of praise, commendation, or admiration; or a courteous greeting or good wishes."
"That dress looks really great on you," O'Neill said. Sam smiled at the compliment, knowing that it took a lot for him to admit it.
"The Minister of Magic sends his compliments," Percy Weasley said as he shook off the rain from his hat.
In verb form, compliment is used to pay a compliment; to show kindness or regard for by a gift or other favor.
"It's not that you are ugly," Ron said, trying desperately to think of a way to compliment Hermione. "It's just that you have dirt and mud all over your face."
Complement on the other hand, is described as "something that completes or makes perfect; or the quantity or amount that completes anything."
The blue in the hat was a perfect complement to Sam's dress, and Daniel liked what he saw.
Jack wasn't worried about running out of bullets. He had a full complement of ammunition at his disposal.
The verb form of complement means "to complete".
Harry, Ron, and Hermione complemented each other--when they combined their talents, they could face anything.
Complement or Compliment?
It can be difficult to remember which word to use as you work on your writing, but it may help to keep in mind that when you want to "complete" something, use complement and save the word, compliment, for "praise".