robe vs vestment

robe and vestment both are nouns.

Word	Noun	Adjective	Verb	Adverb
robe	Yes	No	Yes	No
vestment	Yes	No	No	No

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

robe: outerwear consisting of a long flowing garment used for official or ceremonial occasions
vestment: gown (especially ceremonial garments) worn by the clergy

Other hyponyms of robe include academic gown, academic robe, judge's robe.

robe (noun)	vestment (noun)
any loose flowing garment	gown (especially ceremonial garments) worn by the clergy
outerwear consisting of a long flowing garment used for official or ceremonial occasions

robe (verb)	vestment (verb)
clothe formally; especially in ecclesiastical robes
cover as if with clothing