A rogue Clara's reformed (6)
I believe the answer is:
rascal
'a rogue' is the definition.
(synonyms)
'clara's reformed' is the wordplay.
'reformed' indicates anagramming the letters.
'claras' is an anagram of 'RASCAL'.
(Other definitions for rascal that I've seen before include "not one to be admired" , "A naughty chap or bold boy" , "Michievous person/child" , "Rogue, scamp" , "Villain" .)