New Britain vs island

New Britain and island both are nouns.

Word	Noun	Adjective	Verb	Adverb
New Britain	Yes	No	No	No
island	Yes	No	No	No

New Britain (noun)	island (noun)
the largest island in the Bismarck Archipelago; part of Papua New Guinea	a zone or area resembling an island
	a land mass (smaller than a continent) that is surrounded by water