national capital vs Roma

national capital and Roma both are nouns.

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

national capital (noun)	Roma (noun)
the capital city of a nation	capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire
	a member of a people with dark skin and hair who speak Romany and who traditionally live by seasonal work and fortunetelling; they are believed to have originated in northern India but now are living on all continents (but mostly in Europe, North Africa, and North America)