1. [n]  something added to complete or make perfect; "a fine wine is a perfect complement to the dinner"
2. [n]  either of two parts that mutually complete each other
3. [n]  a word or phrase used to complete a grammatical construction
4. [n]  number needed to make up whole force; "a full complement of workers"
5. [n]  a complete number or quantity; "a full complement"
6. [n]  one of a series of enzymes in the blood serum that are part of the immune response
7. [v]  make complete or perfect; supply what is wanting or form the complement to; "I need some pepper to complement the sweet touch in the soup"

1. \Com"ple*ment\, n. [L. complementun: cf. F.
   compl['e]ment. See {Complete}, v. t., and cf. {Compliment}.]
   1. That which fills up or completes; the quantity or number
      required to fill a thing or make it complete.
   2. That which is required to supply a deficiency, or to
      complete a symmetrical whole.
            History is the complement of poetry.  --Sir J.
                                                  Stephen.
   3. Full quantity, number, or amount; a complete set;
      completeness.
            To exceed his complement and number appointed him
            which was one hundred and twenty persons. --Hakluyt.
   4. (Math.) A second quantity added to a given quantity to
      make it equal to a third given quantity.
   5. Something added for ornamentation; an accessory. [Obs.]
            Without vain art or curious complements. --Spenser.
   6. (Naut.) The whole working force of a vessel.
   7. (Mus.) The interval wanting to complete the octave; -- the
      fourth is the complement of the fifth, the sixth of the
      third.
   8. A compliment. [Obs.] --Shak.
   {Arithmetical compliment of a logarithm}. See under
      {Logarithm}.
   {Arithmetical complement of a number} (Math.), the difference
      between that number and the next higher power of 10; as, 4
      is the complement of 6, and 16 of 84.
   {Complement of an} {arc or angle} (Geom.), the difference
      between that arc or angle and 90[deg].
   {Complement of a parallelogram}. (Math.) See {Gnomon}.
   {In her complement} (Her.), said of the moon when represented
      as full.
   

2. \Com"ple*ment\, v. t.
   1. To supply a lack; to supplement. [R.]
   2. To compliment. [Obs.] --Jer. Taylor.
   

The other value or values in the set of possible values.

See logical complement, bitwise complement, set complement.

1. A protein system that helps antibodies stage a defense against antigens.
2. A biochemical substance (e.g. protein, vitamin, mineral, etc.) that is added to a food to improve its nutritional quality or to correct a deficiency created in cooking or processing.