Britain vs British Isles

Britain and British Isles both are nouns.

Word	Noun	Adjective	Verb	Adverb
Britain	Yes	No	No	No
British Isles	Yes	No	No	No

Britain (noun)	British Isles (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	Great Britain and Ireland and adjacent islands in the north Atlantic