Great Britain vs European Union

Great Britain and European Union both are nouns.

Word	Noun	Adjective	Verb	Adverb
Great Britain	Yes	No	No	No
European Union	Yes	No	No	No

Great Britain (noun)	European Union (noun)
an island comprising England and Scotland and Wales	an international organization of European countries formed after World War II to reduce trade barriers and increase cooperation among its members
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