side·slip / ˈsīdˌslip/ (also side-slip) • n. a sideways skid or slip. ∎ Aeron. a sideways movement of an aircraft, esp. downward toward the inside of a turn. ∎ (in skiing and surfing) an act of traveling down a slope or wave in a direction not in line with one's skis or board.• v. [intr.] skid or slip sideways: the weight counteracts the tire's tendency to sideslip. ∎ Aeron. move in a sideslip. ∎ (in skiing and surfing) travel sideways or in any direction not in line with one's skis or board.