Nihon vs Nippon

Nihon and Nippon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Nihon	Yes	No	No	No
Nippon	Yes	No	No	No

As nouns, Nihon and Nippon are synonyms defined as:

Nihon and Nippon: a constitutional monarchy occupying the Japanese Archipelago; a world leader in electronics and automobile manufacture and ship building

Other synonyms of Nihon include Japan.

Nihon (noun)	Nippon (noun)
a constitutional monarchy occupying the Japanese Archipelago; a world leader in electronics and automobile manufacture and ship building	a constitutional monarchy occupying the Japanese Archipelago; a world leader in electronics and automobile manufacture and ship building