Sentence shortener (6)
I believe the answer is:
parole
'sentence shortener' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for parole that I've seen before include "Conditional release from prison" , "Word - condition of liberty" , "Temporary release on promise of good behaviour" , "Early release on promise of good behaviour" , "Release of prisoner promising good behaviour" .)