National Park Service vs agency

National Park Service and agency both are nouns.

Word	Noun	Adjective	Verb	Adverb
National Park Service	Yes	No	No	No
agency	Yes	No	No	No

As nouns, agency is a hypernym of National Park Service; that is, agency is a word with a broader meaning than National Park Service:

National Park Service: an agency of the Interior Department responsible for the national parks
agency: an administrative unit of government

Other hypernyms of National Park Service include authority, bureau, federal agency, government agency, office.

National Park Service (noun)	agency (noun)
an agency of the Interior Department responsible for the national parks	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