DARPA vs government agency

DARPA and government agency both are nouns.

Word	Noun	Adjective	Verb	Adverb
DARPA	Yes	No	No	No
government agency	Yes	No	No	No

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

DARPA: the central research and development organization for the United States Department of Defense; responsible for developing new surveillance technologies since 9/11
government agency: an administrative unit of government

Other hypernyms of DARPA include agency, authority, bureau, federal agency, office.

DARPA (noun)	government agency (noun)
the central research and development organization for the United States Department of Defense; responsible for developing new surveillance technologies since 9/11	an administrative unit of government