robe vs dressing gown

robe and dressing gown both are nouns.

Word	Noun	Adjective	Verb	Adverb
robe	Yes	No	Yes	No
dressing gown	Yes	No	No	No

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

Other hyponyms of robe include abaya, bathrobe, lounging robe, robe-de-chambre, kimono.

robe (noun)	dressing gown (noun)
any loose flowing garment	a robe worn before dressing or while lounging
outerwear consisting of a long flowing garment used for official or ceremonial occasions

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