United States Army vs office

United States Army and office both are nouns.

Word	Noun	Adjective	Verb	Adverb
United States Army	Yes	No	No	No
office	Yes	No	No	No

As nouns, office is a hypernym of United States Army; that is, office is a word with a broader meaning than United States Army:

United States Army: the army of the United States of America; the agency that organizes and trains soldiers for land warfare
office: an administrative unit of government

Other hypernyms of United States Army include agency, authority, bureau, federal agency, government agency.

United States Army (noun)	office (noun)
the army of the United States of America; the agency that organizes and trains soldiers for land warfare	a religious rite or service prescribed by ecclesiastical authorities
	the actions and activities assigned to or required or expected of a person or group
	a job in an organization
	place of business where professional or clerical duties are performed
	professional or clerical workers in an office
	an administrative unit of government
	(of a government or government official) holding an office means being in power