FDA vs federal agency

FDA and federal agency both are nouns.

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

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

FDA: a federal agency in the Department of Health and Human Services established to regulate the release of new foods and health-related products
federal agency: an administrative unit of government

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

FDA (noun)	federal agency (noun)
a federal agency in the Department of Health and Human Services established to regulate the release of new foods and health-related products	an administrative unit of government