Your spellchecker won’t flag either compliment or complement, but do you know the difference between these two commonly confused terms? Compliment and complement are commonly confused terms because they’re pronounced alike and originally shared some meanings. But over time, they’ve become separate words with entirely different meanings.
Complement with an e is the older of the two terms. Its noun sense has been around in English since the 1300s. The term derives from the Latin complēmentum, meaning “something that completes.” If something complements something else, it completes it, enhances it, or makes it perfect. A shirt can complement the color of someone’s eyes, or a wine can complement a meal. When we talk about complementary angles, or complementary colors, we’re evoking this sense of complement. Complementary angles are two angles that add up to produce a 90° angle. Complementary colors are colors that are directly across each other on the color wheel, and which enhance one another by their contrast, such as red and green, purple and yellow, and blue and orange.
Compliment with an i dates from the mid-1600s. It came to English from the Spanish cumplimiento, by way of Italian and French. Compliment ultimately derives from the same Latin root as complement, complēmentum, which accounts for some of the early overlap in meaning. The noun compliment means “an expression of praise, commendation, or admiration,” and the verb means, “to praise or express admiration for someone.” You can pay someone a compliment, or compliment someone on a job well done. People sometimes use the phrase “compliments to the chef” after enjoying a good meal. Something that is complimentary is free, for examples, airlines offer complimentary sodas on flights.
So how do you keep these two straight? Just remember that if something complements something, it completes it.