pillion

pillion
/ˈpɪlɪən; `pɪljən/ n
seat for a passenger behind the driver of a motor cycle 摩托车後座
    [attrib 作定语]
pillion passenger/seat 摩托车後座坐著的人[座位]. pillion, adv
    ride pillion, ie ride on the pillion 坐在摩托车後座上.

牛津英汉双解词典