European Union with drive set up exchange (8)
I believe the answer is:
dialogue
'exchange' is the definition.
(an exchange of words)
'european union with drive set up' is the wordplay.
'european union' becomes 'eu'.
'with' is a charade indicator (letters next to each other).
'drive' becomes 'go' ('go!' could mean 'drive!').
'set' becomes 'laid' (synonyms).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'eu'+'go'+'laid'='eugolaid'
'eugolaid' back-to-front is 'DIALOGUE'.
(Other definitions for dialogue that I've seen before include "Lines spoken by characters in drama or fiction" , "Two-way conversation" , "Discussion" , "The speech in a play" , "Conversation between two people" .)