complement
Pluralcomplements
Verbcomplements, complementing, complemented
Often confused with compliment
Pluralcomplements
Formscomplements, complementing, complemented
- 1Something that completes another thing or combines with it to form a whole; more loosely, a partner or addition that fits well.
The new wing serves as a fine complement to the existing museum.
Fresh herbs are the ideal complement to a simple bowl of pasta.
Similaraccompaniment, addition, companion, supplement, counterpart
Note
The everyday sense, which takes either of or to. James Stephen wrote in 1854 that "History is the complement of poetry," and The Guardian in 2009 called Kings Place "a complement to the evergreen Wigmore Hall." Of tends to stress two halves of one whole, while to suggests a fitting addition. The word for praise is spelled differently: compliment, with an i.
- 2To supply what another thing lacks while lacking what it supplies, so that the two together form a whole.
The two researchers complement each other, one strong in theory and the other in fieldwork.
Wind and solar power complement each other, since each produces most when the other produces least.
Similarbalance, complete, supplement
Note
This verb is most at home in the reciprocal construction complement each other, used of flavors, talents, two researchers, or wind and solar power. The sense is mutual, since each side supplies what the other lacks, so it suits pairs better than single additions; for those, the plain "complete" verb serves. The adjective for such a pair is complementary.
- 3
- 4The total amount or number that makes something complete; the full quantity required.
With a full complement of staff, the clinic could finally open every day.
The orchestra performed with its complete complement of strings and brass.
Similarquota, allotment, contingent
Note
The root sense of the family, close to the Latin complēmentum, "that which fills up or completes," from compleō, "I fill up." Its signature phrase is full complement. Herman Melville's ship in Moby-Dick (1851) has "her full complement of seamen," and The Guardian in 2009 writes of a council's "complement of 15." The word counts what fills a set, so it usually takes of and a number.
- 5In grammar, a word or phrase that is needed to complete a predicate and that describes or renames the subject or object.
Grammarians classify 'tired' in 'He seems tired' as a subject complement.
A predicate adjective functions as a complement describing the subject.
Note
Grammarians sort complements by what they describe. A subject complement follows a linking verb and refers back to the subject, as tired does in He seems tired. An object complement follows the object and describes it, as captain does in They made her captain. Keep it apart from the object itself: in that sentence her is the object and captain is the complement.
- 6The entire crew needed to operate a ship or other vessel.
The frigate put to sea with a complement of two hundred and forty.
Reduced funding left several vessels short of their normal complement.
Similarcrew, company, personnel
Note
A ship's word for the people who work her: officers and crew together, not the passengers she carries. Because the number is set by what the vessel needs, a ship can sail short of its complement, and that phrase signals a shortage, not merely a small crew. Naval writing also gives it as a bare figure, as in a complement of two hundred and forty.
- 7The angle that, added to a given angle, sums to a right angle of ninety degrees.
Since the angle measures forty degrees, its complement is fifty.
Students learned to calculate the complement of any acute angle.
Note
Geometry and astronomy share this one. Two angles are complements when together they make a right angle, and such a pair is called complementary. Only an acute angle has a complement, since a right or obtuse angle leaves nothing to fill. The Latin sense of "filling up" is still visible here: the complement is what fills the angle out to ninety degrees.
- 8Given two sets, the set of all elements belonging to one set but not to the other.
The complement of set A within the universal set contains everything not in A.
Mathematicians shaded the complement of the overlapping region on the diagram.
Note
Set theory distinguishes two kinds. A relative complement removes one set from another: relative to the natural numbers, the complement of the odd numbers is the even numbers. An absolute complement is taken against a fixed universal set, meaning everything under discussion. Without that background set, the phrase "the complement of A" has no settled meaning, so careful writers state what it is relative to.
- 9The color that, mixed with a given color, produces black when mixing pigments or white when mixing light.
Designers paired each hue with its complement for maximum contrast.
The complement of red light is cyan, and the two together produce white.
Similaropposite
Note
Color theory needs two answers here, because mixing works in two ways. Pigments that are complements darken toward black, while lights that are complements add up to white. Blue and orange make one such pair. In design talk the pair is more often described with the adjective, complementary colors, and valued for the strong contrast it gives when the two sit side by side.
- 10A group of blood proteins that act together with antibodies to support the body's immune response.
When activated, complement helps destroy bacteria by puncturing their cell walls.
The lab measured complement in the serum to assess immune activity.
Note
Immunologists mostly use the word without an article, as a mass noun: complement is activated, and a sample is tested for complement. The name fits the work, because these proteins complement antibodies and help finish what antibodies begin. Activated in a cascade, they mark microbes for destruction and break open their membranes. The system as a whole is simply called complement.
- 11The interval that, combined with a given interval, completes an octave.
A major third and its complement, a minor sixth, together span an octave.
Music students learned to name the complement of each interval.
Similarinversion
Note
Music theory pairs intervals the way geometry pairs angles. Where the geometric sense fills out a right angle, this one fills out an octave. A perfect fourth and a perfect fifth are complements, and so are a major third and a minor sixth. It usually appears in the frame "the complement of" plus an interval name, and the relationship always runs both ways.
- 12The value found by subtracting a number from a power of its base; the two's complement of a binary number, widely used to represent negative values.
Most processors encode signed integers as the two's complement of their magnitude.
Taking the complement and adding one converts a positive binary value into its negative.
Note
Here the possessive is singular, two's complement, because the number is subtracted from a single power of two. Add one to the ones' complement and you reach this one: 01100101 becomes 10011011. Most processors store signed integers this way, so two's complement also names the encoding itself, not only the result of the operation.
- 13A bit holding the opposite value to a given bit; the logical complement, where each one becomes zero and each zero becomes one.
In Boolean logic, the complement of a true value is false.
The NOT gate outputs the complement of its input bit.
Note
Here the complement is taken one bit at a time, which is why programmers call it the logical or bitwise complement and pair it with the NOT operation. Applied across a whole binary number, it turns every one into zero and every zero into one. That gives the same digits as the ones' complement, but logic treats the operation as a flip of truth values, not as arithmetic.
- 14The value found by subtracting each digit from the largest digit of its base; the nines' complement of a decimal number or the ones' complement of a binary one.
In ones' complement arithmetic, the complement of 0101 is 1010.
Engineers once used the nines' complement to perform decimal subtraction.
Note
The apostrophe tells you which family you are in. Nines' and ones' complement are plural possessives, because each digit is subtracted from the largest digit of the base, a nine or a one. In binary this means inverting every bit, so 01100101 becomes 10011010. The result is always exactly one less than the two's complement.
- 15An expression that is true under exactly the conditions that make another expression false, and false when the other is true.
In propositional logic, the complement of a proposition reverses its truth value.
Two expressions that are complements can never both be true at the same time.
Similarnegation
Note
Logic makes the same move as the set-theory complement. Set theory takes everything outside a set; logic takes every situation in which the original expression fails. In practice the complement of an expression is its negation, and the pair divides every case between them: exactly one of the two holds, never both and never neither.
- 16A nucleotide sequence in which each base is replaced by its complementary base: adenine with thymine or uracil, cytosine with guanine, and vice versa.
To find the complement, replace every adenine with thymine and every cytosine with guanine.
The two strands of the double helix are complements of each other.
Note
Molecular biologists use the word for a whole strand: each strand of a DNA molecule is the complement of the other. The pairing rules let anyone write the complement letter by letter, A for T (or U in RNA) and C for G. In the actual double helix, the matching strand also runs in the opposite direction, which is why it is described as antiparallel.
- 17A voltage level carrying the opposite logical sense to a given one, so that a high signal becomes low and a low signal becomes high.
The gate produces the complement of its input, turning a logic high into a logic low.
Digital circuits often route both a signal and its complement to reduce noise.
Similarinverse
- 18A value derived from a given number by a fixed rule on its digits, used so that subtraction can be carried out as addition.
To subtract on paper, you can add the complement of the second number instead.
In two's complement, the complement of a positive value represents its negative.
Note
The general arithmetic sense, used when no particular kind is specified. At its simplest it is the same quantity with the opposite sign: the complement of −123 is 123. The two's complement is one way of encoding exactly that within a fixed number of digits, which is what lets a machine carry out subtraction as addition.
- 19
- 20Abbreviation of complementary good.
Economists describe coffee and cream as complements in consumer demand.
When tea becomes cheaper, sales of its complement, sugar, also rise.
Note
Economics clips complementary good to complement, and the word nearly always comes in pairs: one good is a complement of another, never a complement on its own. The test is demand. When one good of the pair grows more popular or cheaper, its partner sells better too, as games do when consoles spread.
- 21A group of proteins in the blood that work alongside antibodies to mark, attack, and destroy invading microbes and damaged cells.
Activated complement coats the bacterium, marking it for destruction by phagocytes.
A deficiency in complement leaves patients prone to recurrent infections.
Similaralexin
Note
Alexin is the other name for these blood proteins, and the older one; complement is the term that settled. A reader of early biochemistry will meet alexin where a modern text writes complement. The grammar is the same as in the immunologist's protein system, with complement used as a mass noun and no article.
- 22A graphic element that modifies another sign, such as a small syllabic symbol attached to a word-sign in Linear B to indicate part of its reading.
In Linear B, a complement attached to a logogram signals part of its pronunciation.
Epigraphers identify each complement that fixes the reading of a word-sign.
Note
This term comes from the study of scripts that mix word-signs with sound-signs. In Linear B, a logogram may carry a small syllabogram that spells part of its reading, which helps fix the word intended. Specialists keep it distinct from an adjunct, which abbreviates an adjective qualifying the logogram, not the logogram's own reading. The full term, phonetic complement, is the usual one.
- 23Something or someone that completes another; the finishing or crowning element that brings a thing to its fullness.
He saw in her the complement of all his hopes, the crown of his long striving.
Wisdom was held to be the complement of courage, completing the ideal man.
Note
An archaic sense with a loftier ring than the modern one: the complement is the crowning fulfillment, not merely the missing part. Robert Burton, in The Anatomy of Melancholy, calls works of mercy "the extent and complement of love." In present-day prose it reads as deliberately literary. For everyday writing, consummation or the ordinary "completing partner" sense is safer.
- 24Something that completes one's outfit or equipment; an accessory regarded as the finishing piece of a dress or kit.
Garnish'd and deck'd in modest complement,
1599, William Shakespeare, “The Life of Henry the Fift”A man should be judged by himselfe, and not by his complements.
1603, Michel de Montaigne, The EssayesNote
The finery sense of the 1590s and 1600s, usually plural and often faintly suspect. Edmund Spenser wants a song "without vain art or curious complements" (The Teares of the Muses, 1591). Florio's Montaigne (1603) says a man should be judged "by himselfe, and not by his complements," and Shakespeare's Henry V has "modest complement." Read it as accessories, not praise.
- 25The act of completing something, or the state of being complete; completion and fulfillment.
And both encreast the prayse of woman kynde, / And both encreast her beautie excellent: / So all did make in her a perfect complement.
1590, Edmund Spenser, The Faerie QueeneNote
Here the word names a state, not a thing, and that makes it easy to misread. When Edmund Spenser writes "So all did make in her a perfect complement" (The Faerie Queene, 1590), he means perfect completeness. Modern English says completion or fulfillment instead. Used in a present-day sentence, this sense would be taken for the completing partner or for a slip.
- 26Obsolete spelling of compliment, meaning an expression of praise, admiration, or courtesy.
The courtier offered the lady a flattering complement upon her wit.
He received their complements with a modest bow.
Similartribute, accolade, praise
Note
Shakespeare writes "a man of complements" in the 1590s, meaning a man of courtly politeness and flattery rather than one who completes anything. The two words are doublets that both descend from Latin complēmentum, "that which fills up", so their spellings once overlapped. Today the line is firm: compliment means praise and complement means completion. Writing complement for praise now counts as a misspelling.
- 27
Showing meanings only.
Practice
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Origin
From Middle English complement, from Latin complēmentum ("that which fills up or completes"), from compleō ("I fill up, I complete"), which also gives English complete. It is a doublet of compliment, and the verb comes from the noun.