Great Britain vs IR

Great Britain and IR both are nouns.

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

Great Britain (noun)	IR (noun)
an island comprising England and Scotland and Wales	a board of the British government that administers and collects major direct taxes
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