genouillere

from The Century Dictionary.

• noun Milit.: The kneepiece, of hammered iron, introduced toward the close of the thirteenth century, and worn at first over the chausses of mail, being held in place by a strap passing round the leg, and consisting at first of a dish-shaped or slightly pointed roundel.
• noun An articulated piece forming a part of the jambe or of the cuissart in the fourteenth century, and later furnished with large wings which projected backward on each side of the knee-joint.
• noun In fortification: The part of the interior slope of the parapet below the sill of an embrasure, serving to cover the lower part of the gun-carriage.
• noun The height of the parapet above the banquette in a barbette battery.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Anc. Armor) A metal plate covering the knee.
• noun (Fort.) That part of a parapet which lies between the gun platform and the bottom of an embrasure.