Great Britain vs estate of the realm

Great Britain and estate of the realm both are nouns.

Word	Noun	Adjective	Verb	Adverb
Great Britain	Yes	No	No	No
estate of the realm	Yes	No	No	No

Great Britain (noun)	estate of the realm (noun)
an island comprising England and Scotland and Wales	a major social class or order of persons regarded collectively as part of the body politic of the country (especially in the United Kingdom) and formerly possessing distinct political rights
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