Restraint remains supporting the French (5)
I believe the answer is:
leash
'restraint' is the definition.
(leash is a kind of restraint)
'remains supporting the french' is the wordplay.
'remains' becomes 'ash' (I've seen this before).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'the french' becomes 'le'.
'ash' put after 'le' is 'LEASH'.
(Other definitions for leash that I've seen before include "Rope to control dog" , "Line for holding dog" , "Dog lead" , "Strip for leading, a dog say" , "Line for controlling a dog" .)