The Collaborative International Dictionary of English v.0.48:

Conch \Conch\ (k[o^][ng]k), n. [L. concha, Gr. ko`gchh. See
   Coach, n.]
   1. (Zool.) A name applied to various marine univalve shells;
      esp. to those of the genus Strombus, which are of large
      size. Strombus gigas is the large pink West Indian
      conch. The large king, queen, and cameo conchs are of the
      genus Cassis. See Cameo and cameo conch.
      [1913 Webster]

   Note: The conch is sometimes used as a horn or trumpet, as in
         fogs at sea, or to call laborers from work.
         [1913 Webster]

   2. In works of art, the shell used by Tritons as a trumpet.
      [1913 Webster]

   3. [often capitalized] One of the white natives of the Bahama
      Islands or one of their descendants in the Florida Keys;
      -- so called from the commonness of the conch there, or
      because they use it for food.
      [1913 Webster]

   4. (Arch.) See Concha, n.
      [1913 Webster]

   5. The external ear. See Concha, n., 2.
      [1913 Webster]

WordNet (r) 3.0 (2006):

conch
    n 1: any of various edible tropical marine gastropods of the
         genus Strombus having a brightly-colored spiral shell with
         large outer lip