IR vs Great Britain

IR and Great Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
IR	Yes	No	No	No
Great Britain	Yes	No	No	No

IR (noun)	Great Britain (noun)
a board of the British government that administers and collects major direct taxes	an island comprising England and Scotland and Wales
	a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom