Manhattan Island vs New York City

Manhattan Island and New York City both are nouns.

Word	Noun	Adjective	Verb	Adverb
Manhattan Island	Yes	No	No	No
New York City	Yes	No	No	No

Manhattan Island (noun)	New York City (noun)
an island at the north end of New York Bay where the borough of Manhattan is located	the largest city in New York State and in the United States; located in southeastern New York at the mouth of the Hudson river; a major financial and cultural center