roundel vs armour plate

roundel and armour plate both are nouns.

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

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

roundel: round piece of armor plate that protects the armpit
armour plate: specially hardened steel plate used to protect fortifications or vehicles from enemy fire

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

roundel (noun)	armour plate (noun)
round piece of armor plate that protects the armpit	specially hardened steel plate used to protect fortifications or vehicles from enemy fire
(heraldry) a charge in the shape of a filled circle
English form of rondeau having three triplets with a refrain after the first and third