Business opposed to European scientific collaboration (7)
I believe the answer is:
concern
'business' is the definition.
(eg 'none of your concern', 'none of your business')
'opposed to european scientific collaboration' is the wordplay.
'opposed to' becomes 'con' (as in pros and cons).
'european scientific collaboration' becomes 'CERN' (nuclear research centre).
'con'+'cern'='CONCERN'
(Other definitions for concern that I've seen before include "Business - anxiety" , "Affect; solicitude" , "Business organisation" , "Involve" , "Firm - interest" .)