helmet vs armor plate

helmet and armor plate both are nouns.

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

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

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

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

helmet (noun)	armor 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