Constant criticism curtailed at parting (6)
I believe the answer is:
static
'constant' is the definition.
(I've seen this before)
'criticism curtailed at parting' is the wordplay.
I cannot really understand how this works, but
'at' is within the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for static that I've seen before include "Unmoving like kind of electricity" , "Lacking movement or action" , "stable" , "Inactive or inert" , "irritation for the listener?" .)