Britain vs third estate

Britain and third estate both are nouns.

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

Britain (noun)	third 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 common people