National Guard Bureau vs agency

National Guard Bureau and agency both are nouns.

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

As nouns, agency is a hypernym of National Guard Bureau; that is, agency 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
agency: an administrative unit of government

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

National Guard Bureau (noun)	agency (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	to have the ability to produce a particular effect or achieve an end
	an administrative unit of government
	a business or organization that provides a particular service, especially the mediation of transactions between two parties
	the state of serving as an official and authorized delegate or agent
	the state of being in action or exerting power