The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. That which is required to supply a deficiency, or to
      complete a symmetrical whole.
      [1913 Webster]

            History is the complement of poetry.  --Sir J.
                                                  Stephen.
      [1913 Webster]

   3. Full quantity, number, or amount; a complete set;
      completeness.
      [1913 Webster]

            To exceed his complement and number appointed him
            which was one hundred and twenty persons. --Hakluyt.
      [1913 Webster]

   4. (Math.) A second quantity added to a given quantity to
      make it equal to a third given quantity.
      [1913 Webster]

   5. Something added for ornamentation; an accessory. [Obs.]
      [1913 Webster]

            Without vain art or curious complements. --Spenser.
      [1913 Webster]

   6. (Naut.) The whole working force of a vessel.
      [1913 Webster]

   7. (Mus.) The interval wanting to complete the octave; -- the
      fourth is the complement of the fifth, the sixth of the
      third.
      [1913 Webster]

   8. A compliment. [Obs.] --Shak.
      [1913 Webster]

   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 Complement of an 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.
      [1913 Webster]