complement

Etymology

It is borrowed from Latin complēmentum (“that which fills up or completes”),^{[2][3][4][5][6]} formed on compleō (“to fill up, complete”) with the suffix -mentum (-ment).^[2][7][8] The American Heritage Dictionary, Barnhart and Etymonline take it through compliement (“accomplishment, fulfilment”),^[9][4][3] while the OED derives it without a French step and notes only a single 14th-century instance of the French complément.^[2] The Latin verb is formed with com-, here probably intensive, on pleō (“to fill”),^[3][6] which Etymonline traces to Proto-Indo-European *pelh₁- (“to fill”).^[3] It is the same Latin word as compliment, which came later through French and Italian; the two are doublets.^[4][6][5][2]

Earliest recorded meaning

That which completes or makes perfect; the completion or consummation of something: 1398, in John Trevisa's translation of Bartholomew's De Proprietatibus Rerum.^[2][4] The action of fulfilling or completing is recorded from 1419, a sense now obsolete.^[2]

Semantic evolution

In the 16th century the word took on courtly senses: something added as an ornament rather than out of need, a personal accomplishment, and the observance of ceremony or a tribute of courtesy.^[3][10] Between about 1655 and 1725 these senses passed to the parallel French word compliment, and the two spellings were then kept apart.^[2] The verb shows the same split: it meant to exchange formal courtesies from a1625 (1612 in Barnhart) and to flatter from 1649, senses now expressed by compliment,^[2][4][3] while the sense that survives, to make complete or to form the complement to something, is recorded from 1643.^[2][4] Merriam-Webster dates the transitive verb to 1602.^[8] The idea of a full quantity gave the senses "complete set or allowance" (1589) and the full number needed to man a ship (1600).^[2] Technical uses followed in mathematics (1570), astronomy (1703) and grammar (1874).^[2] In Cornwall and Leicestershire dialect complement meant the usual quantity, the right amount.^[11] Johnson (1755) defined it as perfection, fullness or completion, and the full quantity.^[12]

Timeline

• 1398 – that which completes or makes perfect.^[2][4]
• 1419 – completion, fulfilment (obsolete).^[2]
• 1570 – in mathematics.^[2]
• 1589 – the full quantity or set.^[2]
• 1600 – the full number needed to man a ship.^[2]
• a1625 – verb, to exchange formal courtesies (obsolete).^[2]
• 1643 – verb, to complete or form the complement to.^[2]
• 1703 – in astronomy, the difference between an angle and 90 degrees.^[2]
• 1827 – each of two parts that complete each other.^[2]
• 1874 – in grammar, words that complete the sense.^[2]

Modern meaning

Noun

1. A thing that completes something or makes it perfect; one of two parts that together form a whole or make up for each other's lacks: The sharp cheese is a fine complement to the sweet wine.
2. The full number or quantity needed, especially the officers and crew of a ship: The ship sailed with its full complement of crew.
3. (grammar) A word or phrase that completes a predicate, such as a noun or adjective after a copula.
4. (mathematics) The amount by which an angle falls short of 90 degrees; the angle that must be added to it to make a right angle.
5. (immunology) A group of proteins in blood serum that help antibodies destroy bacteria and other cells.

Verb

1. To complete something or make it better by adding what it lacks; to go well with: The new curtains complement the colour of the walls.

Word family

• complementer
• complemental
• object complement
• subject complement
• two's complement

Related words

• complementary
• complete
• compliment
• counterpart
• supplement
• plenty

Usage notes

Dictionary.com has a usage note on complement and compliment, which are often confused.^[7] It also contrasts complement with supplement: to complement is to supply something felt to be lacking, to supplement is to add to something already complete.^[7]

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r s t u Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e f g Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
5. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
6. ^ a b c Skeat, Walter W. (1911), A Concise Etymological Dictionary of the English Language, new ed., Oxford: Clarendon Press
7. ^ a b c Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
8. ^ a b Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
9. ^ The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
10. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
11. ^ Wright, Joseph, ed. (1898–1905), The English Dialect Dictionary, 6 vols., Oxford: Henry Frowde; via EDD Online 4.0, University of Innsbruck (CC BY 4.0)
12. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.