01 n. 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.
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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.” — Spenser.
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2.
A saddle or seat behind the driver's saddle on a motorcycle, used by passengers.