European Union vs EEC

European Union and EEC both are nouns.

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

As nouns, European Union and EEC are synonyms defined as:

European Union and EEC: an international organization of European countries formed after World War II to reduce trade barriers and increase cooperation among its members

Other synonyms of European Union include Common Market, EC, EU, Europe, European Community, European Economic Community.

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