roundel vs plate armour

roundel and plate armour both are nouns.

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

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

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

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

roundel (noun)	plate armour (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a charge in the shape of a filled circle	a historical type of personal armor made from iron or steel plates, which superseded mail during the 14th century.
English form of rondeau having three triplets with a refrain after the first and third