UK vs European Union

UK and European Union both are nouns.

Word	Noun	Adjective	Verb	Adverb
UK	Yes	No	No	No
European Union	Yes	No	No	No

UK (noun)	European Union (noun)
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	an international organization of European countries formed after World War II to reduce trade barriers and increase cooperation among its members