NIH vs federal agency

NIH and federal agency both are nouns.

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

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

NIH: an agency in the Department of Health and Human Services whose mission is to employ science in the pursuit of knowledge to improve human health; is the principal biomedical research agency of the federal government
federal agency: an administrative unit of government

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

NIH (noun)	federal agency (noun)
an agency in the Department of Health and Human Services whose mission is to employ science in the pursuit of knowledge to improve human health; is the principal biomedical research agency of the federal government	an administrative unit of government