n. [ Ir. pillin, pilliun (akin to Gael. pillean, pillin), fr. Ir. & Gael. pill, peall, a skin or hide, prob. fr. L. 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. [ 1913 Webster ]
His [ a soldier's ] shank pillion without stirrups. Spenser. [ 1913 Webster ]
2. A saddle or seat behind the driver's saddle on a motorcycle, used by passengers. [ PJC ]