[noun kom-pluh-muh nt; verb kom-pluh-ment]


verb (used with object)

to complete; form a complement to: This belt complements the dress better than that one.
Obsolete. to compliment.

verb (used without object)

Obsolete. to compliment.

Nearby words

  1. compleat,
  2. compleat angler, the,
  3. complect,
  4. complected,
  5. complection,
  6. complement binding assay,
  7. complement clause,
  8. complement fixation,
  9. complement fixation test,
  10. complement protein

Origin of complement

1350–1400; Middle English < Latin complēmentum something that completes, equivalent to complē(re) to fill up (see complete) + -mentum -ment

Related formscom·ple·ment·er, noun

Can be confusedcomplement supplement (see synonym study at the current entry)complement compliment (see usage note at the current entry)

Synonym study

12. Complement, supplement both mean to make additions to something. To complement is to provide something felt to be lacking or needed; it is often applied to putting together two things, each of which supplies what is lacking in the other, to make a complete whole: Two statements from different points of view may complement each other. To supplement is merely to add to: Some additional remarks may supplement his address.

Usage note

Complement and compliment, which are pronounced alike and originally shared some meanings, have become separate words with entirely different meanings. As a noun, complement means “something that completes or makes perfect”: The rare old brandy was a perfect complement to the delicious meal. As a verb, complement means “to complete”: A bright scarf complements a dark suit. The noun compliment means “an expression of praise, commendation, or admiration”: The members paid her the compliment of a standing ovation. The verb compliment means “to pay a compliment to”: Everyone complimented him after the recital. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for complement

British Dictionary definitions for complement


noun (ˈkɒmplɪmənt)

a person or thing that completes something
one of two parts that make up a whole or complete each other
a complete amount, number, etc (often in the phrase full complement)
the officers and crew needed to man a ship
  1. a noun phrase that follows a copula or similar verb, as for example an idiot in the sentence He is an idiot
  2. a clause that serves as the subject or direct object of a verb or the direct object of a preposition, as for example that he would be early in the sentence I hoped that he would be early
maths the angle that when added to a specified angle produces a right angle
logic maths the class of all things, or of all members of a given universe of discourse, that are not members of a given set
music the inverted form of an interval that, when added to the interval, completes the octavethe sixth is the complement of the third
immunol a group of proteins in the blood serum that, when activated by antibodies, causes destruction of alien cells, such as bacteria

verb (ˈkɒmplɪˌmɛnt)

(tr) to add to, make complete, or form a complement to

Word Origin for complement

C14: from Latin complēmentum, from complēre to fill up, from com- (intensive) + plēre to fill


Avoid confusion with compliment

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for complement
Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for complement




A group of proteins found in normal blood serum and plasma that are activated sequentially in a cascadelike mechanism that allows them to combine with antibodies and destroy pathogenic bacteria and other foreign cells.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for complement



A group of proteins in blood serum that interact systematically as part of the body's immune response to destroy disease-causing antigens, especially bacteria. Complement proteins interact with antibodies and other chemical substances to cause the disintegration of foreign cells and enhance other immune functions such as phagocytosis.
A complementary color.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.