island vs Great Britain

island and Great Britain both are nouns.

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

island (noun)	Great Britain (noun)
a zone or area resembling an island	an island comprising England and Scotland and Wales
a land mass (smaller than a continent) that is surrounded by water	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