Source : Webster's Revised Unabridged Dictionary (1913)

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

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