Wine the French rejected drunk by agent (7)
I believe the answer is:
moselle
'wine' is the definition.
(Moselle is an example)
'the french rejected drunk by agent' is the wordplay.
'the french' becomes 'les' (plural form of 'the' in French).
'rejected' is a reversal indicator.
'drunk by' means one lot of letters goes inside another.
'agent' becomes 'mole' (mole is a kind of agent).
'les' back-to-front is 'sel'.
'sel' placed inside 'mole' is 'MOSELLE'.
(Other definitions for moselle that I've seen before include "River; white wine" , "Light white wine" , "French or German white wine" , "French department" , "Fr. river, department; German wine" .)