IRS vs Treasury Department

IRS and Treasury Department both are nouns.

Word	Noun	Adjective	Verb	Adverb
IRS	Yes	No	No	No
Treasury Department	Yes	No	No	No

IRS (noun)	Treasury Department (noun)
the bureau of the Treasury Department responsible for tax collections	the federal department that collects revenue and administers federal finances; the Treasury Department was created in 1789