copper's nark vs United Kingdom of Great Britain and Northern Ireland

copper's nark and United Kingdom of Great Britain and Northern Ireland both are nouns.

Word	Noun	Adjective	Verb	Adverb
copper's nark	Yes	No	No	No
United Kingdom of Great Britain and Northern Ireland	Yes	No	No	No

copper's nark (noun)	United Kingdom of Great Britain and Northern Ireland (noun)
an informer or spy working for the police	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