The French put off diminishing (5)
I believe the answer is:
let-up
'diminishing' is the definition.
'the french put off' is the subsidiary indication.
'the french' becomes 'le'.
'off' is an anagram indicator.
'put' with letters rearranged gives 'tup'.
'le'+'tup'='letup'
(Other definitions for let-up that I've seen before include "Respite, relief" , "Pause in intensity" , "Relieving pause" , "Abatement" , "Pause, temporary respite" .)