In set theory, a complement of a set A refers to things not in A. The relative complement of A with respect to a set B, is the set of elements in B but not in A. When all sets under consideration are considered to be subsets of a given set U, the absolute complement of A is the set of all elements in U but not in A.

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  1. Something (or someone) that completes; the consummation.
  2. The act of completing something, or the fact of being complete; completion, completeness, fulfilment.
  3. The totality, the full amount or number which completes something.
  4. Something which completes one's equipment, dress etc.; an accessory.
  5. The whole working force of a vessel.
  6. Fullness (of the moon).
  7. An angle which, together with a given angle, makes a right angle.
  8. Something which completes, something which combines with something else to make up a complete whole; loosely, something perceived to be a harmonious or desirable partner or addition.
  9. A word or group of words that completes a grammatical construction in the predicate and that describes or is identified with the subject or object.
  10. An interval which, together with the given interval, makes an octave.
  11. The color which, when mixed with the given color, gives black (for mixing pigments) or white (for mixing light).
    The complement of blue is orange.
  12. Given two sets, the set containing one set's elements that are not members of the other set (whether a relative complement or an absolute complement).
    The complement of the odd numbers is the even numbers, relative to the natural numbers.
  13. One of several blood proteins that work with antibodies during an immune response.
  14. An expression related to some other expression such that it is true under the same conditions that make other false, and vice versa.
  15. A voltage level with the opposite logical sense to the given one.
  16. A bit with the opposite value to the given one; the logical complement of a number.
  17. The diminished radix complement of a number; the nines' complement of a decimal number; the ones' complement of a binary number.
    The complement of <math>01100101_2</math> is <math>10011010_2</math>.
  18. The radix complement of a number; the two's complement of a binary number.
    The complement of <math>01100101_2</math> is <math>10011011_2</math>.
  19. The numeric complement of a number.
    The complement of -123 is 123.
  20. A nucleotide sequence in which each base is replaced by the complementary base of the given sequence: adenine (A) by thymine (T) or uracil (U), cytosine (C) by guanine (G), and vice versa.
    A DNA molecule is formed from two strands, each of which is the complement of the other.


  1. To complete, to bring to perfection, to make whole.
    We believe your addition will complement the team.
  2. To provide what the partner lacks and lack what the partner provides.
    The flavors of the pepper and garlic complement each other, giving a very rich taste in combination.
    I believe our talents really complement each other.
  3. To change a voltage, number, color, etc. to its complement.

The above text is a snippet from Wiktionary: complement
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