Great Britain vs common room

Great Britain and common room both are nouns.

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

Great Britain (noun)	common room (noun)
an island comprising England and Scotland and Wales	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