The quality of being complementary; the state of completing or enhancing something else perfectly.
From 'complementary' (from Latin 'complementum,' meaning 'something that completes,' from 'complere' 'to fill up') + '-ness'. Note the spelling: 'complement' (meaning to complete), not 'compliment' (meaning to praise).
English speakers constantly confuse 'complement' and 'compliment,' but the etymology tells the tale—'complement' comes from Latin 'complere' (to fill), while 'compliment' comes from French 'complir' (to complete a courtesy), making them false cognates that diverged in meaning centuries ago.
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