United States Capitol vs Capitol Building

United States Capitol and Capitol Building both are nouns.

Word	Noun	Adjective	Verb	Adverb
United States Capitol	Yes	No	No	No
Capitol Building	Yes	No	No	No

As nouns, United States Capitol and Capitol Building are synonyms defined as:

United States Capitol and Capitol Building: the government building in Washington where the United States Senate and the House of Representatives meet

Other synonyms of United States Capitol include Capitol.

United States Capitol (noun)	Capitol Building (noun)
the government building in Washington where the United States Senate and the House of Representatives meet	the government building in Washington where the United States Senate and the House of Representatives meet