kneepiece

from The Century Dictionary.

• noun Same as knee-rafter.
• noun An angular piece of timber used in a roof to strengthen a joint where two timbers meet.
• noun Milit., any defensive appliance used to cover the knee; especially, in medieval armor, the genouillère. See cut under genouillère.
• noun In ship-building, same as knee, 3 .

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

• noun A piece shaped like a knee.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The piece of armour that covers the knee.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun armor plate that protects the knee