Inland Revenue vs IR

Inland Revenue and IR both are nouns.

Word	Noun	Adjective	Verb	Adverb
Inland Revenue	Yes	No	No	No
IR	Yes	No	No	No

As nouns, Inland Revenue and IR are synonyms defined as:

Inland Revenue and IR: a board of the British government that administers and collects major direct taxes

Inland Revenue (noun)	IR (noun)
a board of the British government that administers and collects major direct taxes	a board of the British government that administers and collects major direct taxes