breastplate vs armour plate

breastplate and armour plate both are nouns.

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

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

breastplate: armor plate that protects the chest; the front part of a cuirass
armour plate: specially hardened steel plate used to protect fortifications or vehicles from enemy fire

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

breastplate (noun)	armour plate (noun)
armor plate that protects the chest; the front part of a cuirass	specially hardened steel plate used to protect fortifications or vehicles from enemy fire