fish·tail / ˈfishˌtāl/ • n. [usu. as adj.] an object that is forked like a fish's tail: carved detail including fishtail terminals on the banisters. ∎ an uncontrolled sideways movement of the back of a motor vehicle: he hit the brakes, sending the car into a fishtail that carried him across the street.• v. [intr.] (of a vehicle) make such a movement: the vehicle fishtailed from one side of the road to the other. ∎ [tr.] cause (a vehicle) to make such a movement: Carson fishtailed the Mercedes out into the road.