Washington vs Capital

Washington and Capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
Washington	Yes	No	No	No
Capital	Yes	No	No	No

As nouns, Washington and Capital are synonyms defined as:

Washington (noun)	Capital (noun)
the federal government of the United States	a book written by Karl Marx (1867) describing his economic theories
a state in northwestern United States on the Pacific with capital Olympia	the federal government of the United States
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
1st President of the United States; commander-in-chief of the Continental Army during the American Revolution (1732-1799)
United States educator who was born a slave but became educated and founded a college at Tuskegee in Alabama (1856-1915)