Spelling Thursday: Complement and Compliment

Complement (v. and n.) -- to enhance or add extra features to make something better. 'That tomato sauces complements my dinner.' Also, as a noun: 'Your new purple hat is the perfect complement to your ball gown.'
Complement (n.) -- the number needed to complete a group: 'We have a full complement at the moment. Couldn't jam another sailor in if you tried.'

Compliment (v.) -- say something nice about someone. And this is the word to use if you're thinking of 'compliment slips'. 'May I compliment you on your choice of purple hat and ball gown?'
Complimentary (adj.) -- free of charge. 'Here's your complimentary moist towelette.'

There's a 'lime' in the middle of the 'saying something nice' and 'free gift' compliment, so perhaps you can fix in your head the idea of praising a small green citrus fruit which someone has given you for free.