The Collaborative International Dictionary of English v.0.48:

Chin \Chin\ (ch[i^]n), n. [AS. cin, akin to OS. kin, G kinn,
   Icel. kinn, cheek, Dan. & Sw. kind, L. gena, Gr. ?; cf.
   Skr. hanu. [root]232.]
   1. The lower extremity of the face below the mouth; the point
      of the under jaw.
      [1913 Webster]

   2. (Zool.) The exterior or under surface embraced between the
      branches of the lower jaw bone, in birds.
      [1913 Webster]

WordNet (r) 3.0 (2006):

chin
    n 1: the protruding part of the lower jaw [syn: chin,
         mentum]
    2: Kamarupan languages spoken in western Burma and Bangladesh
       and easternmost India [syn: Kuki, Chin, Kuki-Chin]
    v 1: raise oneself while hanging from one's hands until one's
         chin is level with the support bar [syn: chin, chin up]