helmet vs armour plate

helmet and armour plate both are nouns.

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

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

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

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

helmet (noun)	armour plate (noun)
a protective headgear made of hard material to resist blows	specially hardened steel plate used to protect fortifications or vehicles from enemy fire
armor plate that protects the head