plate armor vs brassard

plate armor and brassard both are nouns.

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

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

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

plate armor (noun)	brassard (noun)
specially hardened steel plate used to protect fortifications or vehicles from enemy fire	armor plate that protects the arm
a historical type of personal armor made from iron or steel plates, which superseded mail during the 14th century.