Customs Service vs agency

Customs Service and agency both are nouns.

Word	Noun	Adjective	Verb	Adverb
Customs Service	Yes	No	No	No
agency	Yes	No	No	No

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

Customs Service: the agency of the Treasury Department that enforces import tariffs
agency: an administrative unit of government

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

Customs Service (noun)	agency (noun)
the agency of the Treasury Department that enforces import tariffs	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