IR vs administrative unit

IR and administrative unit both are nouns.

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

As nouns, administrative unit is a hypernym of IR; that is, administrative unit is a word with a broader meaning than IR:

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

Other hypernyms of IR include administrative body.

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