EEC vs European Union

EEC and European Union both are nouns.

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

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

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

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

EEC (noun)	European Union (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