Allows English leader to overturn ban by the French (7)
I believe the answer is:
enables
'allows' is the definition.
(I've seen this before)
'english leader to overturn ban by the french' is the wordplay.
'leader' suggests taking the first letters.
'to overturn' is a reversal indicator.
'by' means one lot of letters go next to another.
'the french' becomes 'les' (plural form of 'the' in French).
The first letter of 'english' is 'e'.
'ban' in reverse letter order is 'nab'.
'e'+'nab'+'les'='ENABLES'
(Other definitions for enables that I've seen before include "Renders capable" , "Allows" , "Makes possible" , "Facilitates or empowers" .)