second estate vs United Kingdom of Great Britain and Northern Ireland

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

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

second estate (noun)	United Kingdom of Great Britain and Northern Ireland (noun)
the nobility in France and the peerage 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