PILLION, a light saddle without pommel or bow, especially a pad fastened to the back of an ordinary saddle, as a seat for another person, generally a woman. Pillions were also used to support baggage. They were in common use from the 16th to the 18th centuries. The word appears to have been adapted into English from the Irish pillin, cushion, formed from Lat. pellis, skin. In the sense of a hat worn by a priest or doctor of divinity, " pillon " or " pylion " occurs in the isth and 16th centuries. This is probably from Lat. pileus, a conical felt hat or cap, Gr. mXos.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)