United Kingdom of Great Britain and Northern Ireland vs common room

United Kingdom of Great Britain and Northern Ireland and common room both are nouns.

Word	Noun	Adjective	Verb	Adverb
United Kingdom of Great Britain and Northern Ireland	Yes	No	No	No
common room	Yes	No	No	No

United Kingdom of Great Britain and Northern Ireland (noun)	common room (noun)
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	a sitting room (usually at school or university)