Definition of complement in English:

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Pronunciation: /ˈkämpləmənt/
1A thing that completes or brings to perfection: the libretto proved a perfect complement to the music
More example sentences
  • And I'm going to start off a new occasional feature, a complement to my ‘How Not to Do It’ series of lab stories.
  • Many retailers are also becoming more active in the seed business or are partnering with seed companies, so seed treatment as a whole is a great complement to and natural extension of the seed business.
  • As a complement to the board's oversight, FDA will improve transparency by sharing drug safety information sooner and more broadly and conveniently.
accompaniment, companion, addition, supplement, accessory, trimming
2 [in singular] A number or quantity of something required to make a group complete: at the moment we have a full complement of staff
More example sentences
  • This will require a full complement of diplomatic, political and military efforts.
  • The cell is then stretched and split into two halves on the framework of microtubules, each half containing a full complement of chromosomes.
  • Tetraploids, inheriting a full complement of chromosomes from each parent, and thus having double the normal allowance, occur in nature or can be induced.
amount, total, contingent, capacity, allowance, quota
2.1The number of people required to crew a ship: almost half the ship’s complement of 322 were wounded
More example sentences
  • Each ship will have a complement of typically 1,200, including 600 air crew.
  • The ship's complement is 210 crew with 13 officers.
  • Eliminating meals will also mean the normal complement of cabin crew can be cut from six to three.
2.2 Geometry The amount in degrees by which a given angle is less than 90°.
2.3 Mathematics The members of a set that are not members of a given subset.
Example sentences
  • Likewise, in base 2, the complement of a number is obtained by subtraction from a row of 1's.
3 Grammar One or more words, phrases, or clauses governed by a verb (or by a nominalization or a predicative adjective) that complete the meaning of the predicate.
Example sentences
  • Complement clauses are subordinate clauses that function as complements of a word: that they were too noisy in She told them that they were too noisy.
  • Recall that a verb governs an object, and the head of a phrase governs the complement.
  • For many people, ‘feel like’ has become a complex verb that takes sentential complements.
3.1(In systemic grammar) an adjective or noun that has the same reference as either the subject (as mad in he is mad) or the object (as mad in he drove her mad).
4 Physiology A group of proteins present in blood plasma and tissue fluid that combine with an antigen-antibody complex to bring about the lysis of foreign cells.
Example sentences
  • An example is a transfusion reaction in which IgG and IgM anti-red-cell antibodies activate complement and cause cell lysis.
  • Red blood cell susceptibility to complement was ruled out via a negative sucrose hemolysis test thus precluding a diagnosis of PNH.16
  • The DAT is usually positive, confirming the presence of IgG antibodies with or without complement on the red cells.


Pronunciation: /ˈkämpləˌment/
[with object]
1Add to (something) in a way that enhances or improves it; make perfect: a classic blazer complements a look that’s stylish or casual
More example sentences
  • This capability complements policy-based management features that allow automated or advised actions, based on conditions detected through advanced diagnostics.
  • Riding last year's breakthrough, he's using slightly improved on-base skills to complement his power-speed combination.
  • There was something about his personality that lent itself to New York, a stubborn quality that complements a stubborn city.
accompany, go with, round off, set off, suit, harmonize with;
enhance, complete
1.1Add to or make complete: the proposals complement the incentives already available
More example sentences
  • The Nubira complements the already strong line up of Matiz, Kalos and Tacuma.
  • Bosses at Pizza Pioneer, which in July will celebrate its 16th anniversary, have decided to open during the day to complement its already buoyant evening business.
  • I am pleased to hear that a good variety of businesses have made the decision to locate here and this will complement the already thriving business community locally.


Complement and compliment (together with related words such as complementary and complimentary) are frequently confused. They are pronounced in the same way but have quite different meanings: as a verb, complement means ‘add to something in a way that enhances or improves,’ as in a classic blazer complements a look that’s smart or casual, while compliment means ‘admire and praise someone for something,’ as in he complimented her on her appearance. Complementary means ‘forming a complement or addition, completing,’ as in I purchased a suit with a complementary tie. This is often confused with complimentary, for which one sense is ‘given freely, as a courtesy’: honeymooners receive complimentary fruit and flowers.



Pronunciation: /ˌkämpləˈmentl/
Example sentences
  • These distinctions between replacement and complemental were particularly marked at seven points.
  • Of course, the question of how a dwarf or complemental male finds an appropriate host to house him still remains.
  • The affinity between the mutually complemental antibody and receptor was described by a weighted affinity matrix.


Late Middle English (in the sense 'completion'): from Latin complementum, from complere 'fill up' (see complete). Compare with compliment.

For editors and proofreaders

Syllabification: com·ple·ment

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