Answer: pillion

AnswerCrossword Clue
PILLIONCushion for lady passenger on horseback.
PILLIONCushion behind a saddle.
pillionpad or cushion attached behind a saddle, esp. as a seat for a woman
pillionpad, cushion, saddle, or the like, used as a passenger seat on a bicycle, motor scooter, etc.
pillionpassenger's saddle or seat behind the driver's seat on a motorcycle
pillionto sit on a pillion (a passenger seat)