# complement

Pronunciation: say "KOM-pluh-muhnt" US /ˈkɑmpləmənt/, UK /ˈkɒmpləmənt/

## Noun

1. Something that completes another thing or combines with it to form a whole; more loosely, a partner or addition that fits well.
   - Simple: A thing that goes well with another and helps make it complete.
   - _The new wing serves as a fine complement to the existing museum._
   - _Fresh herbs are the ideal complement to a simple bowl of pasta._
4. The total amount or number that makes something complete; the full quantity required.
   - Simple: The full number or amount needed to make something complete.
   - _With a full complement of staff, the clinic could finally open every day._
   - _The orchestra performed with its complete complement of strings and brass._
5. In grammar, a word or phrase that is needed to complete a predicate and that describes or renames the subject or object.
   - Simple: A word or group of words that finishes a sentence by telling more about 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._
6. The entire crew needed to operate a ship or other vessel.
   - Simple: The full group of people needed to run a ship.
   - _The frigate put to sea with a complement of two hundred and forty._
   - _Reduced funding left several vessels short of their normal complement._
7. The angle that, added to a given angle, sums to a right angle of ninety degrees.
   - Simple: The angle that adds to another to make 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._
8. Given two sets, the set of all elements belonging to one set but not to the other.
   - Simple: The set of items that are in one group but not in 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._
9. The color that, mixed with a given color, produces black when mixing pigments or white when mixing light.
   - Simple: The color that mixes with another to make black or white.
   - _Designers paired each hue with its complement for maximum contrast._
   - _The complement of red light is cyan, and the two together produce white._
10. A group of blood proteins that act together with antibodies to support the body's immune response.
   - Simple: Blood proteins that work with antibodies to fight infection.
   - _When activated, complement helps destroy bacteria by puncturing their cell walls._
   - _The lab measured complement in the serum to assess immune activity._
11. The interval that, combined with a given interval, completes an octave.
   - Simple: The musical interval that adds to another to make a full octave.
   - _A major third and its complement, a minor sixth, together span an octave._
   - _Music students learned to name the complement of each interval._
12. The 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.
   - Simple: A way of writing a number by subtracting it from a power of its base, used to store negative numbers.
   - _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._
13. A bit holding the opposite value to a given bit; the logical complement, where each one becomes zero and each zero becomes one.
   - Simple: A bit flipped to its opposite value, so a one becomes a zero and a zero becomes a one.
   - _In Boolean logic, the complement of a true value is false._
   - _The NOT gate outputs the complement of its input bit._
14. The 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.
   - Simple: A number formed by subtracting each digit from the top digit of its base.
   - _In ones' complement arithmetic, the complement of 0101 is 1010._
   - _Engineers once used the nines' complement to perform decimal subtraction._
15. An expression that is true under exactly the conditions that make another expression false, and false when the other is true.
   - Simple: A statement that is true exactly when another statement is 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._
16. A nucleotide sequence in which each base is replaced by its complementary base: adenine with thymine or uracil, cytosine with guanine, and vice versa.
   - Simple: A strand of DNA or RNA in which each base is paired with its matching opposite base.
   - _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._
17. A voltage level carrying the opposite logical sense to a given one, so that a high signal becomes low and a low signal becomes high.
   - Simple: A voltage that stands for the opposite logic value: high instead of low, or low instead of 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._
18. A value derived from a given number by a fixed rule on its digits, used so that subtraction can be carried out as addition.
   - Simple: A number made from another one so that the two add up to a round number like ten or a hundred.
   - _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._
20. Abbreviation of complementary good. — Abbreviation of complementary good.
   - Simple: Short form of complementary good. A product you tend to buy and use together with another.
   - _Economists describe coffee and cream as complements in consumer demand._
   - _When tea becomes cheaper, sales of its complement, sugar, also rise._
21. A group of proteins in the blood that work alongside antibodies to mark, attack, and destroy invading microbes and damaged cells.
   - Simple: A group of blood proteins that help the immune system find and destroy germs.
   - _Activated complement coats the bacterium, marking it for destruction by phagocytes._
   - _A deficiency in complement leaves patients prone to recurrent infections._
22. A 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.
   - Simple: In old writing systems, a small sign added to a word-sign to show part of how it should be read.
   - _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._
26. Obsolete spelling of compliment, meaning an expression of praise, admiration, or courtesy.
   - Simple: An old way to spell compliment, a kind remark that praises someone.
   - _The courtier offered the lady a flattering complement upon her wit._
   - _He received their complements with a modest bow._

## Verb

2. To supply what another thing lacks while lacking what it supplies, so that the two together form a whole.
   - Simple: To go well with something by adding what it is missing.
   - _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._
3. To complete something or bring it to perfection, making it whole.
   - Simple: To make something whole or bring it to its best state.
   - _The closing speech complemented the ceremony and brought the day to a fitting end._
   - _These final touches complement the design and complete the overall effect._
19. To change a voltage, number, color, or similar value to its complement.
   - Simple: To change a number, voltage, or color into its opposite matching value.
   - _To get the negative value, complement the number and then add one._
   - _The function complements every pixel to produce a photographic negative._
27. Obsolete spelling of compliment, meaning to praise or flatter someone with courteous remarks.
   - Simple: An old way to spell compliment, to say kind words that praise someone.
   - _He rose to complement the bride on her beauty._
   - _The critics complemented the young poet for his daring verses._

## Noun

23. Something or someone that completes another; the finishing or crowning element that brings a thing to its fullness. *(archaic)*
   - Simple: Someone or something that completes another and makes it whole.
   - _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._
24. Something that completes one's outfit or equipment; an accessory regarded as the finishing piece of a dress or kit. *(obsolete)*
   - Simple: An item that completes someone's clothing or gear, like an accessory.
25. The act of completing something, or the state of being complete; completion and fulfillment. *(obsolete)*
   - Simple: The act of finishing something, or the state of being finished.

## 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.

Source: DictionaryAI, https://dictionaryai.com/define/complement (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).