The Collaborative International Dictionary of English v.0.48:

coonskin \coonskin\ n.
   a cap made from the skin of a raccoon, with the tail hanging
   down the back; -- called also coonskin cap.

   Syn: coonskin cap.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

coonskin
    n 1: a raccoon cap with the tail hanging down the back [syn:
         coonskin cap, coonskin]