double first vs Britain

double first and Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
double first	Yes	No	No	No
Britain	Yes	No	No	No

double first (noun)	Britain (noun)
a first-class honours degree in two subjects	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