Source : Webster's Revised Unabridged Dictionary (1913)

Labrum \La"brum\, n.; pl. L. {Labra}, E. {Labrums}. [L.]
   1. A lip or edge, as of a basin.

   2. (Zo["o]l.)
      (a) An organ in insects and crustaceans covering the upper
          part of the mouth, and serving as an upper lip. See
          Illust. of {Hymenoptera}.
      (b) The external margin of the aperture of a shell. See
          {Univalve}.