common room vs Britain

common room and Britain both are nouns.

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

common room (noun)	Britain (noun)
a sitting room (usually at school or university)	a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom