Britain vs mere

Britain and mere both are nouns.

Word	Noun	Adjective	Verb	Adverb
Britain	Yes	No	No	No
mere	Yes	Yes	No	No

Britain (noun)	mere (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	a small pond of standing water

Britain (adjective)	mere (adjective)
	apart from anything else; without additions or modifications
	being nothing more than specified