Criminal depressed by long sentence (7)
I believe the answer is:
lowlife
'criminal' is the definition.
(I've seen this before)
'depressed by long sentence' is the wordplay.
'depressed' becomes 'low' (synonyms).
'by' is a charade indicator (letters next to each other).
'long sentence' becomes 'life' (life in prison).
'low'+'life'='LOWLIFE'
(Other definitions for lowlife that I've seen before include "Member(s) of the underworld" , "disreputable sort" , "Disreputable character" , "Corrupt" , "criminal" .)