The Collaborative International Dictionary of English v.0.48:

Scapegoat \Scape"goat`\, n. [Scape (for escape) + goat.]
   1. (Jewish Antiq.) A goat upon whose head were symbolically
      placed the sins of the people, after which he was suffered
      to escape into the wilderness. --Lev. xvi. 10.
      [1913 Webster]

   2. Hence, a person or thing that is made to bear blame for
      others. --Tennyson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

scapegoat
    n 1: someone who is punished for the errors of others [syn:
         scapegoat, whipping boy]