national capital vs Ottawa

national capital and Ottawa both are nouns.

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

national capital (noun)	Ottawa (noun)
the capital city of a nation	the capital of Canada (located in southeastern Ontario across the Ottawa river from Quebec)
	a river in southeastern Canada that flows along the boundary between Quebec and Ontario to the Saint Lawrence River near Montreal
	a member of the Algonquian people of southern Ontario