plate armour vs egis

plate armour and egis both are nouns.

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

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

plate armour: specially hardened steel plate used to protect fortifications or vehicles from enemy fire
egis: armor plate that protects the chest; the front part of a cuirass

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a historical type of personal armor made from iron or steel plates, which superseded mail during the 14th century.