Potomac vs American capital

Potomac and American capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
Potomac	Yes	No	No	No
American capital	Yes	No	No	No

Potomac (noun)	American capital (noun)
term sometimes used to refer to Washington, D.C.	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
a river in the east central United States; rises in West Virginia in the Appalachian Mountains and flows eastward, forming the boundary between Maryland and Virginia, to the Chesapeake Bay