Common Market vs European Union

Common Market and European Union both are nouns.

Word	Noun	Adjective	Verb	Adverb
Common Market	Yes	No	No	No
European Union	Yes	No	No	No

As nouns, Common Market and European Union are synonyms defined as:

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

Common Market (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