knee piece vs armour plate

knee piece and armour plate both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee piece	Yes	No	No	No
armour plate	Yes	No	No	No

As nouns, armour plate is a hypernym of knee piece; that is, armour plate is a word with a broader meaning than knee piece:

knee piece: armor plate that protects the knee
armour plate: specially hardened steel plate used to protect fortifications or vehicles from enemy fire

Other hypernyms of knee piece include armor plate, armor plating, plate armor, plate armour.

knee piece (noun)	armour plate (noun)
armor plate that protects the knee	specially hardened steel plate used to protect fortifications or vehicles from enemy fire