office vs government agency

office and government agency both are nouns.

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

As nouns, office and government agency are synonyms defined as:

Other synonyms of office include agency, authority, bureau, federal agency.

office (noun)	government agency (noun)
a religious rite or service prescribed by ecclesiastical authorities	an administrative unit of government
the actions and activities assigned to or required or expected of a person or group
a job in an organization
place of business where professional or clerical duties are performed
professional or clerical workers in an office
an administrative unit of government
(of a government or government official) holding an office means being in power