Great Britain vs subtopia

Great Britain and subtopia both are nouns.

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

Great Britain (noun)	subtopia (noun)
an island comprising England and Scotland and Wales	monotonous urban sprawl of standardized buildings
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