District of Columbia vs American capital

District of Columbia and American capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
District of Columbia	Yes	No	No	No
American capital	Yes	No	No	No

District of Columbia (noun)	American capital (noun)
the district occupied entirely by the city of Washington; chosen by George Washington as the site of the capital of the United States and created out of land ceded by Maryland and Virginia	the capital of the United States in the District of Columbia and a tourist mecca; George Washington commissioned Charles L'Enfant to lay out the city in 1791