complement

1 of 2

noun

com·​ple·​ment ˈkäm-plə-mənt 

1

a

: something that fills up, completes, or makes better or perfect

The scarf is a perfect complement to her outfit.

b(1)

: the full quantity, number, or assortment needed or included

… the usual complement of eyes and ears …

—Francis Parkman

… after several more minutes of waiting, the full complement of runners was sent off by the starter's pistol.

—Craig Neff

(2)

: the whole force or personnel of a ship

c

: one of two mutually completing parts : counterpart

She is a kind of complement to me, and we get on famously.

—Flannery O'Connor

Note: Do not confuse complement with compliment. Complement shares its first two syllables with the word complete, and its meanings relate to completion, as in "a tangy sauce that complements the rich dessert" and "artwork that is a perfect complement to the room's decor." Meanwhile, compliment implies communication, as in "guests complimenting us on the meal" and "compliments to the chef."

2

grammar : an added word or expression by which a predication is made complete (such as mayor in "they elected her mayor" and beautiful in "I thought the music beautiful")

3

mathematics

a

: the angle or arc that when added to a given angle or arc equals a right angle in measure

b

: the set of all elements that do not belong to a given set and are contained in a particular mathematical set containing the given set

c

: a number that when added to a certain number of the same sign yields a number with the digit 1 as the significant digit farthest to the left and the digit 0 in every other digit place

—used especially in assembly language programming

4

: the musical interval required with a given interval to complete the octave

5

medical : the thermolabile group of proteins in normal blood serum and plasma that in combination with antibodies causes the destruction especially of particulate antigens (such as bacteria and foreign blood corpuscles)

Illustration of complement

• ACB right angle
• ACD complement of DCB (and vice versa)
• AD complement of DB (and vice versa)

complement

2 of 2

verb

com·​ple·​ment ˈkäm-plə-ˌment 

complemented; complementing; complements

transitive verb

1

: to complete or enhance by providing something additional : to be complementary to

The illustrations complement the text.

2

obsolete : compliment

intransitive verb

obsolete : to exchange formal courtesies

Did you know?

Is it complement or compliment?

Today there is no overlap between the meanings of complement and compliment, as either nouns or verbs, but their similar spellings and pronunciations make them prime candidates for confusion. Despite the difference in their meanings, both complement and compliment have roots in the Latin word complēre which means “to complete.” Complement remains true to that origin in its spelling and in its meanings that have to do with completing or completion. Keep that connection in mind and there should be no question as to whether complement or compliment is the correct word to use in a given context.

Synonyms of complement

Noun

• supplement

Verb

• adorn
• enhance
• complete
• decorate
• improve

Examples of complement in a Sentence

Noun

With the loss of just one American and four Japanese carriers, including their complements of aircraft and many of their superbly trained fliers …  , Midway … put the Japanese navy at a disadvantage from which it never recovered. —David M. Kennedy, Atlantic, March 1999

Exact observation of the outer world was the complement to a literal reading of Scripture. —Garry Wills, Under God, 1990

The usual complement of Kremlin guards was about, one company of infantry with light arms. —Tom Clancy, Red Storm Rising, 1986

His faults are accepted as the necessary complement to his merits. —W. Somerset Maugham, Moon and Sixpence, 1919

The scarf is a perfect complement to her outfit.

a full complement of farm animals

her usual complement of attendants

a ship's complement of officers

“President” in “they elected her president” and “to work” in “he wants to work” are different kinds of complements.

Verb

Carrots often work even better than sticks, so I propose a skinny subsidy to complement the fat tax. —Jonathan Rauch, Atlantic, December 2002

The love of Bottom's bottomless vision at least complements, if it does not transcend, the rational love of Theseus. —Frank Kermode, Shakespeare's Language, 2000

… his ice-blue Appalachian eyes glint through horn-rimmed glasses, which complement his salt-and-pepper beard. —Henry Louis Gates, Jr., New Yorker, 19 June 1995

… lively photographs, illustrations and cartoons designed to complement the meanings of the poems and give a leg-up to the imagination. —Carol Ann Duffy, Times Literary Supplement, 4-10 Dec. 1987

The shirt complements the suit nicely.

a delicious dinner complemented by a splendid dessert

The soup and salad complement each other well.

Recent Examples on the Web

Noun

New Mexico offers a longer window to enjoy fall foliage and one signature event that provides a unique complement to the season takes place in Taos, about an hour north of Sante Fe. — Jeanne Bonner, CNN Money, 7 Oct. 2026

Their arrival brought the station up to its normal complement of seven crewmembers. — Mike Wall, Space.com, 6 Oct. 2026

Verb

For that reason, Siegel sees AI as more likely to complement the shopping experience than replace it. — Alexa Lomonaco, CNBC, 9 Oct. 2026

Canada’s artificial intelligence talent, research capabilities, and energy resources complement those of the United States, just as its resources and manufacturing did in the twentieth century. — Robert B. Zoellick, Foreign Affairs, 9 Oct. 2026

Word History

Etymology

Noun

Middle English, "means of completing, consummation," borrowed from Anglo-French & Latin; Anglo-French, "carrying out" (also continental Middle French), borrowed from Latin complēmentum "something that fills out or completes," from complēre "to fill, make up, carry to completion" + -mentum -ment — more at complete entry 1

Note: See note at compliment entry 1.

Verb

derivative of complement entry 1

First Known Use

Noun

14th century, in the meaning defined at sense 1a

Verb

1602, in the meaning defined at intransitive sense

Phrases Containing complement

• complement fixation
• objective complement
• subjective complement
• two's complement

Kids Definition

complement

1 of 2 noun

com·​ple·​ment ˈkäm-plə-mənt 

1

: something that fills up, completes, or makes perfect

2

: full quantity, number, or amount

a ship's complement of officers and crew

3

a

: the angle that when added to a given angle equals 90 degrees

b

: the set of all elements not included in a given mathematical set

4

: an added word or group of words by which the predicate of a sentence is made complete

"president" in "they elected her president" and "to work" in "he wants to work" are different kinds of complements

5

: a heat-sensitive substance in normal blood that in combination with antibodies destroys antigens (as bacteria and foreign blood corpuscles)

complement

2 of 2 verb

com·​ple·​ment ˈkäm-plə-ˌment 

: to form or serve as a complement to

a shirt that complements a suit

Medical Definition

complement

noun

com·​ple·​ment ˈkäm-plə-mənt 

1

: a group or set (as of chromosomes or DNA) that is typical of the complete organism or one of its parts see chromosome complement

2

: a complementary color

3

: the thermolabile group of proteins in normal blood serum and plasma that in combination with antibodies causes the destruction especially of particulate antigens (as bacteria and foreign blood corpuscles)