Great Britain vs supremo

Great Britain and supremo both are nouns.

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

Great Britain (noun)	supremo (noun)
an island comprising England and Scotland and Wales	the most important person in an organization
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