National Guard Bureau vs bureau

National Guard Bureau and bureau both are nouns.

Word	Noun	Adjective	Verb	Adverb
National Guard Bureau	Yes	No	No	No
bureau	Yes	No	No	No

As nouns, bureau is a hypernym of National Guard Bureau; that is, bureau is a word with a broader meaning than National Guard Bureau:

National Guard Bureau: the agency that administers the Army National Guard and the Air National Guard; provides liaison between the Army and the Air Force and various National Guard units
bureau: an administrative unit of government

Other hypernyms of National Guard Bureau include agency, authority, federal agency, government agency, office.

National Guard Bureau (noun)	bureau (noun)
the agency that administers the Army National Guard and the Air National Guard; provides liaison between the Army and the Air Force and various National Guard units	furniture with drawers for keeping clothes
	an administrative unit of government