Source : Webster's Revised Unabridged Dictionary (1913)

Bushwhacker \Bush"whack`er\, n.
   1. One accustomed to beat about, or travel through, bushes.
      [U.S.]

            They were gallant bushwhackers, and hunters of
            raccoons by moonlight.                --W. Irving.

   2. A guerrilla; a marauding assassin; one who pretends to be
      a peaceful citizen, but secretly harasses a hostile force
      or its sympathizers. [U.S.] --Farrow.

Source : WordNet®

bushwhacker
     n 1: a disparaging term for an unsophisticated person [syn: {hillbilly}]
     2: a Confederate guerrilla during the American Civil War