wash room vs men's room

wash room and men's room both are nouns.

Word	Noun	Adjective	Verb	Adverb
wash room	Yes	No	No	No
men's room	Yes	No	No	No

As nouns, men's room is a hyponym of wash room; that is, men's room is a word with a more specific, narrower meaning than wash room:

Other hyponyms of wash room include ladies' room, powder room, latrine, men's.

wash room (noun)	men's room (noun)
a toilet that is available to the public	a public toilet for men