What's the difference?
Well, even I’ve been caught out on this one, so if it’s got me, I’m sure it’s got a few of you too. And then there’s those students learning English…
Okay, so here are the differences according to the Collins Cobuild Dictionary, but rewritten in my own way.
Compliment with an ‘i’
We’ll start with the more well-known definition, and so this means compliment with the ‘i’ and not the ‘e’. This version – compliment - is something nice that you say to someone because you like the way they look, or the clothes they wear, or the qualities they bring, or you just generally approve of them and what they’ve done. When you do this, you’re complimenting them or giving them a compliment: He complemented her on the fantastic job she did. He was happy she gave him a compliment on the excellent job.
Now if someone says something or does something that convinces you of your qualities – even if they appear to be negative – then you would consider it a compliment. For example: Well, at least she likes your cooking, so you should consider that a compliment.
Finally on this version of compliment (with an i), it can used as a plural noun to express your thanks, respect or just to wish someone well: My compliments to the chef! That was excellent!
Complement (with an ‘e’)
This verb and noun is usually around two things in the sense that they are a kind of combination. Let’s break the meanings down:
The word has a similar meaning to enhance, complete or boost - that is, if one thing is a match for another, it’s good and makes its positive features more obvious: I think Yorkshire Pudding complements roast beef (or is an excellent complement to roast beef). If these people or things complement each other, they make a good combination even if they are different or do something different: There’ll be biscuits to complement the coffee. With your brains and my money, we complement each other nicely!
The word does have a different meaning in the sense that it describes the normal number of something to make something work properly: The hotel has a complement of 40 staff. The building doesn’t have its full complement of windows installed.
It’s also a grammar word, so see NOT4GRAMMARBORES.