common room vs Great Britain

common room and Great Britain both are nouns.

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

common room (noun)	Great Britain (noun)
a sitting room (usually at school or university)	an island comprising England and Scotland and Wales
	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