United Kingdom of Great Britain and Northern Ireland vs first estate

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

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

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