Wiktionary
n. The part of medieval armour that protected the knee
Wikipedia
The poleyn was a component of Medieval and Renaissance armor that protected the knee. During the transition from mail armor to plate armor, this was among the earliest plate components to develop. They first appeared in the mid-thirteenth century and remained in use until the early seventeenth century when firearms made them obsolete.
The specifics of poleyn design varied considerably over that period. The earliest poleyns were strapped over mail chausses. Fourteenth century and early fifteenth century poleyns usually attached to padded leggings or plate cuisses. During the fifteenth century poleyns developed an articulated construction that attached to the cuisses and schynbalds or greaves. A characteristic of late fifteenth century gothic armor was a projection that guarded the side of the knee.
Usage examples of "poleyn".
Raoul looked at the stones, pulling a handkerchief from under the poleyn that covered his right knee to wipe his face.
And whenever he donned chainmail and breastplate, and the hooped iron skirt and the cuisses and poleyns and greaves, and the plated gauntlets and the heavy stuffy visored helmet, not forgetting the heraldic surcoat which was his badge of identification, so as to take on any band of Bruce’s Scots who came a-raiding, he fought them like a junior Hercules, cleaving and battering.
The machine squealed loudly as its crown-wheels tried to pull him deeper inside, and the teeth of its cogs rattled against his poleyns, or knee-plates.