The Collaborative International Dictionary of English v.0.48:

Labrum \La"brum\, n.; pl. L. Labra, E. Labrums. [L.]
   1. A lip or edge, as of a basin.
      [1913 Webster]

   2. (Zool.)
      (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.
          [1913 Webster]