dressing room vs room

dressing room and room both are nouns.

Word	Noun	Adjective	Verb	Adverb
dressing room	Yes	No	No	No
room	Yes	No	Yes	No

As nouns, room is a hypernym of dressing room; that is, room is a word with a broader meaning than dressing room:

dressing room (noun)	room (noun)
a room in which you can change clothes	an area within a building enclosed by walls and floor and ceiling
	the people who are present in a room
	space for movement
	opportunity for

dressing room (verb)	room (verb)
	live and take one's meals at or in