OSHA vs government agency

OSHA and government agency both are nouns.

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

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

OSHA: a government agency in the Department of Labor to maintain a safe and healthy work environment
government agency: an administrative unit of government

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

OSHA (noun)	government agency (noun)
a government agency in the Department of Labor to maintain a safe and healthy work environment	an administrative unit of government