Come out of European Union? Not entirely (6)
I believe the answer is:
emerge
'come out' is the definition.
(synonyms)
'of european union? not entirely' is the wordplay.
'of european' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'union?' becomes 'merger' (merger is a kind of union).
'not entirely' means to remove the last letter (not all of the word).
'merger' with its final letter taken away is 'merge'.
'e'+'merge'='EMERGE'
Can you help me to learn more?
(Other definitions for emerge that I've seen before include "Come forth or appear" , "Come into existence" , "Issue" , "Come out or transpire" , "Gradually come out" .)