island vs South Island

island and South Island both are nouns.

Word	Noun	Adjective	Verb	Adverb
island	Yes	No	No	No
South Island	Yes	No	No	No

island (noun)	South Island (noun)
a zone or area resembling an island	the larger but less populous of two main islands of New Zealand; separated from North Island by Cook Strait
a land mass (smaller than a continent) that is surrounded by water