The Collaborative International Dictionary of English v.0.48:

Concha \Con"cha\ (k[o^][ng]"k[.a]), n. [LL. (in sense 1), fr. L.
   concha. See Conch.]
   1. (Arch.) The plain semidome of an apse; sometimes used for
      the entire apse.
      [1913 Webster]

   2. (Anat.) The external ear; esp. the largest and deepest
      concavity of the external ear, surrounding the entrance to
      the auditory canal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

concha
    n 1: (anatomy) a structure that resembles a shell in shape