Set up European missile business (5)
I believe the answer is:
trade
'business' is the definition.
(trade is a kind of business)
'set up european missile' is the wordplay.
'set up' says the letters should be written in reverse.
'european' becomes 'e' (abbreviation e.g. EU).
'missile' becomes 'dart' (dart is a kind of missile).
'e'+'dart'='edart'
'edart' in reverse letter order is 'TRADE'.
(Other definitions for trade that I've seen before include "Skilled occupation" , "Commercial dealings" , "Buy and sell in business" , "Rated (anag.)" , "Dealing in goods" .)