Powerless at university to arrest the French (6)
I believe the answer is:
unable
'powerless' is the definition.
('unable' can be similar in meaning to 'powerless')
'at university to arrest the french' is the wordplay.
'at' is a charade indicator (letters next to each other).
'university' becomes 'u'.
'to arrest' becomes 'nab' ('nab' can be a synonym of 'arrest'**).
'the french' becomes 'le'.
'u'+'nab' is 'unab'.
'unab'+'le'='UNABLE'
(Other definitions for unable that I've seen before include "Lacking the skill" , "Not having the necessary means or skill or know-how" , "Not fit or competent" , "Not capable" , "Lacking the required capacity" .)