Great Britain vs strongroom

Great Britain and strongroom both are nouns.

Word	Noun	Adjective	Verb	Adverb
Great Britain	Yes	No	No	No
strongroom	Yes	No	No	No

Great Britain (noun)	strongroom (noun)
an island comprising England and Scotland and Wales	a burglarproof and fireproof room in which valuables are kept
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