national capital vs Athinai

national capital and Athinai both are nouns.

Word	Noun	Adjective	Verb	Adverb
national capital	Yes	No	No	No
Athinai	Yes	No	No	No

national capital (noun)	Athinai (noun)
the capital city of a nation	the capital and largest city of Greece; named after Athena (its patron goddess)