South Island vs New Zealand Islands

South Island and New Zealand Islands both are nouns.

Word	Noun	Adjective	Verb	Adverb
South Island	Yes	No	No	No
New Zealand Islands	Yes	No	No	No

South Island (noun)	New Zealand Islands (noun)
the larger but less populous of two main islands of New Zealand; separated from North Island by Cook Strait	North Island and South Island and adjacent small islands in the South Pacific