Source : Webster's Revised Unabridged Dictionary (1913)

Labium \La"bi*um\, n.; pl. L. {Labia}, E. {Labiums}. [L.]
   1. A lip, or liplike organ.

   2. The lip of an organ pipe.

   3. pl. (Anat.) The folds of integument at the opening of the
      vulva.

   4. (Zo["o]l.)
      (a) The organ of insects which covers the mouth beneath,
          and serves as an under lip. It consists of the second
          pair of maxill[ae], usually closely united in the
          middle line, but bearing a pair of palpi in most
          insects. It often consists of a thin anterior part
          (ligula or palpiger) and a firmer posterior plate
          (mentum).
      (b) Inner margin of the aperture of a shell.

Labia \La"bi*a\, n. pl.
   See {Labium}.

Source : WordNet®

labium
     n : any of the four lip-shaped folds of the female vulva
     [also: {labia} (pl)]

labia
     See {labium}