Don's cruel -- naughty rascal (9)
I believe the answer is:
scoundrel
'rascal' is the definition.
(thesaurus)
'don's cruel naughty' is the wordplay.
'naughty' is an anagram indicator.
'dons'+'cruel'='donscruel'
'donscruel' with letters rearranged gives 'SCOUNDREL'.
(Other definitions for scoundrel that I've seen before include "Knave" , "bad egg" , "Rascal" , "Hound" , "Person that's low" .)