The Collaborative International Dictionary of English v.0.48:

Copperhead \Cop"per*head`\, n. [From its color.]
   1. (Zool.) A poisonous American serpent (Ancistrodon
      conotortrix), closely allied to the rattlesnake, but
      without rattles; -- called also copper-belly, and red
      viper.
      [1913 Webster]

   2. A nickname applied to a person in the Northern States who
      sympathized with the South during the Civil War. [U.S.]
      [1913 Webster]