common room vs parlour

common room and parlour both are nouns.

Word	Noun	Adjective	Verb	Adverb
common room	Yes	No	No	No
parlour	Yes	No	No	No

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

common room: a sitting room (usually at school or university)
parlour: a room in a private house or establishment where people can sit and talk and relax

Other hypernyms of common room include front room, living-room, living room, parlor, sitting room.

common room (noun)	parlour (noun)
a sitting room (usually at school or university)	reception room in an inn or club where visitors can be received
	a room in a private house or establishment where people can sit and talk and relax