pig·gy·back / ˈpigēˌbak/ • n. a ride on someone's back and shoulders.• adv. on the back and shoulders of another person: he had to carry him piggyback. ∎ on top of something else: Dave headed back with the car riding piggyback on his truck.• v. [tr.] carry by or as if by piggyback. ∎ mount on or attach to (an existing object or system): providers of information have piggybacked their own networks onto the system. ∎ [intr.] use existing work or an existing product as a basis or support: we were piggybacking on their training program.• adj. on the back and shoulders of another person: enjoying a piggyback ride. ∎ attached to or riding on a larger object: a telescope with fittings for piggyback cameras and guidescopes | fig. a piggyback income tax, under which taxpayers would pay the state 21 percent of whatever they paid the federal government.