breastplate vs aegis

breastplate and aegis both are nouns.

Word	Noun	Adjective	Verb	Adverb
breastplate	Yes	No	No	No
aegis	Yes	No	No	No

As nouns, breastplate and aegis are synonyms defined as:

breastplate and aegis: armor plate that protects the chest; the front part of a cuirass

Other synonyms of breastplate include egis.

breastplate (noun)	aegis (noun)
armor plate that protects the chest; the front part of a cuirass	kindly endorsement and guidance
	armor plate that protects the chest; the front part of a cuirass