Source : Webster's Revised Unabridged Dictionary (1913)

Complemental \Com`ple*men"tal\, a.
   1. Supplying, or tending to supply, a deficiency; fully
      completing. ``Complemental ceremony.'' --Prynne.

   2. Complimentary; courteous. [Obs.] --Shak.

   {Complemental air} (Physiol.), the air (averaging 100 cubic
      inches) which can be drawn into the lungs in addition to
      the tidal air, by the deepest possible inspiration.

   {Complemental males} (Zo["o]l.), peculiar small males living
      parasitically on the ordinary hermaphrodite individuals of
      certain barnacles.

Source : WordNet®

complemental
     adj : acting as or providing a complement (something that
           completes the whole) [syn: {complementary}, {completing}]