Italian vs Neapolitan

Italian and Neapolitan both are nouns.

Word	Noun	Adjective	Verb	Adverb
Italian	Yes	Yes	No	No
Neapolitan	Yes	Yes	No	No

As nouns, Neapolitan is a hyponym of Italian; that is, Neapolitan is a word with a more specific, narrower meaning than Italian:

Italian (noun)	Neapolitan (noun)
the Romance language spoken in Italy	a native or inhabitant of Naples
a native or inhabitant of Italy

Italian (adjective)	Neapolitan (adjective)
of or pertaining to or characteristic of Italy or its people or culture or language	of or relating to or characteristic of Naples or its people