first estate vs United Kingdom of Great Britain and Northern Ireland

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

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

first estate (noun)	United Kingdom of Great Britain and Northern Ireland (noun)
the clergy in France and the heads of the church in Britain	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