armor plating vs helmet

armor plating and helmet both are nouns.

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

As nouns, helmet is a hyponym of armor plating; that is, helmet is a word with a more specific, narrower meaning than armor plating:

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

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