Bushwhackers
a term applied during the Civil War to loose, irregular characters, particularly of the southwest. When at home they professed to be neutrals, sympathizing with neither army. As a matter of practice, they hid away in ambush and shot passing soldiers, or, like ordinary bandits, held up travelers for their valuables. It is difficult to draw the line between a bushwhacker, a guerilla, and a highwayman.
Volume I · Aiton’s Encyclopedia