administrative unit vs IR

administrative unit and IR both are nouns.

Word	Noun	Adjective	Verb	Adverb
administrative unit	Yes	No	No	No
IR	Yes	No	No	No

As nouns, IR is a hyponym of administrative unit; that is, IR is a word with a more specific, narrower meaning than administrative unit:

administrative unit: a unit with administrative responsibilities
IR: a board of the British government that administers and collects major direct taxes

administrative unit (noun)	IR (noun)
a unit with administrative responsibilities	a board of the British government that administers and collects major direct taxes