The Collaborative International Dictionary of English v.0.48:

Chiton \Chi"ton\, n. [Gr. ? a chiton (in sense 1).]
   1. An under garment among the ancient Greeks, nearly
      representing the modern shirt.
      [1913 Webster]

   2. (Zool.) One of a group of gastropod mollusks, with a shell
      composed of eight movable dorsal plates. See
      Polyplacophora.
      [1913 Webster]

WordNet (r) 3.0 (2006):

chiton
    n 1: a woolen tunic worn by men and women in ancient Greece
    2: primitive elongated bilaterally symmetrical marine mollusk
       having a mantle covered with eight calcareous plates [syn:
       chiton, coat-of-mail shell, sea cradle,
       polyplacophore]