Nippon vs Japanese capital

Nippon and Japanese capital both are nouns.

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

Nippon (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