billiard room vs room

billiard room and room both are nouns.

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

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

billiard room (noun)	room (noun)
a room in which billiards is played	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

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