undergarment vs vest

undergarment and vest both are nouns.

Word	Noun	Adjective	Verb	Adverb
undergarment	Yes	No	No	No
vest	Yes	No	Yes	No

As nouns, vest is a hyponym of undergarment; that is, vest is a word with a more specific, narrower meaning than undergarment:

undergarment (noun)	vest (noun)
a garment worn under other garments	a collarless men's undergarment for the upper part of the body
	a man's sleeveless garment worn underneath a coat

undergarment (verb)	vest (verb)
	clothe formally; especially in ecclesiastical robes
	clothe oneself in ecclesiastical garments
	place (authority, property, or rights) in the control of a person or group of persons
	become legally vested
	provide with power and authority