A compliment with an I is an expression of praise. A complement with an E completes something or pairs well with it — the sauce complements the fish. The mnemonic: complEment complEtes; complIment is somethIng nice.
The core difference
Praise and completion, one vowel apart.
- compliment (I) — praise: pay her a compliment, a complimentary review.
- complement (E) — completes or pairs well: the wine complements the meal.
The free sense
Complimentary also means free of charge — a complimentary breakfast. That is the praise word, from the idea of a courteous gift. Complementary with an E means going well together — complementary colours, complementary skills. A hotel offering "complementary breakfast" is claiming the meal completes you.
The technical senses
Complement does precise work in grammar (completing a verb's meaning), geometry (angles totalling 90 degrees) and immunology (the complement system). All use the completing sense.
Frequently asked questions
Is it complimentary or complementary breakfast?
Complimentary, with an I — it means free of charge.
How do I remember which is which?
ComplEment complEtes. ComplIment is somethIng nice.
What are complementary colours?
Colours that go well together, using the completing sense with an E.