third estate vs Great Britain

third estate and Great Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
third estate	Yes	No	No	No
Great Britain	Yes	No	No	No

third estate (noun)	Great Britain (noun)
the common people	an island comprising England and Scotland and Wales
	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