Pillion
Pillion , noun
[Ir. pillin, pilliun (akin to Gael. pillean, pillin), from Ir. & Gael. pill, peall, a skin or hide, prob. from Latin pellis. See Pell, n., Fell skin.]
1.
A panel or cushion saddle; the under pad or cushion of saddle; esp., a pad or cushion put on behind a man's saddle, on which a woman may ride.
His [a soldier's] shank pillion without stirrups.
2.
A saddle or seat behind the driver's saddle on a motorcycle, used by passengers.