Internal Revenue Service vs IRS

Internal Revenue Service and IRS both are nouns.

Word	Noun	Adjective	Verb	Adverb
Internal Revenue Service	Yes	No	No	No
IRS	Yes	No	No	No

As nouns, Internal Revenue Service and IRS are synonyms defined as:

Internal Revenue Service and IRS: the bureau of the Treasury Department responsible for tax collections

Internal Revenue Service (noun)	IRS (noun)
the bureau of the Treasury Department responsible for tax collections	the bureau of the Treasury Department responsible for tax collections