Source : Webster's Revised Unabridged Dictionary (1913)

Complement \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.