backplate vs armour plate

backplate and armour plate both are nouns.

Word	Noun	Adjective	Verb	Adverb
backplate	Yes	No	No	No
armour plate	Yes	No	No	No

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

backplate: plate armor protecting the back; worn as part of a cuirass
armour plate: specially hardened steel plate used to protect fortifications or vehicles from enemy fire

Other hypernyms of backplate include armor plate, armor plating, plate armor, plate armour.

backplate (noun)	armour plate (noun)
plate armor protecting the back; worn as part of a cuirass	specially hardened steel plate used to protect fortifications or vehicles from enemy fire