DARPA vs federal agency

DARPA and federal agency both are nouns.

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

As nouns, federal agency is a hypernym of DARPA; that is, federal 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
federal agency: an administrative unit of government

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

DARPA (noun)	federal 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