Nihon vs Japanese capital

Nihon and Japanese capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
Nihon	Yes	No	No	No
Japanese capital	Yes	No	No	No

Nihon (noun)	Japanese capital (noun)
a constitutional monarchy occupying the Japanese Archipelago; a world leader in electronics and automobile manufacture and ship building	the capital and largest city of Japan; the economic and cultural center of Japan