Son: a cruel, wicked criminal (9)
I believe the answer is:
larcenous
'criminal' is the definition.
(I've seen this before)
'son a cruel wicked' is the wordplay.
'wicked' indicates anagramming the letters.
'son'+'a'+'cruel'='sonacruel'
'sonacruel' anagrammed gives 'LARCENOUS'.
(Other definitions for larcenous that I've seen before include "Related to theft" , "Thievish" , "Relating to theft" , "Inclined to appropriate" , "concerning certain crimes" .)