supremo vs United Kingdom of Great Britain and Northern Ireland

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

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

supremo (noun)	United Kingdom of Great Britain and Northern Ireland (noun)
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