Once a slur about criminal (9)
I believe the answer is:
larcenous
'criminal' is the definition.
(I've seen this before)
'once a slur about' is the wordplay.
'about' is an anagram indicator.
'once'+'a'+'slur'='onceaslur'
'onceaslur' anagrammed gives 'LARCENOUS'.
(Other definitions for larcenous that I've seen before include "Inclined to appropriate" , "Inclined to steal" , "Relating to theft" , "Criminal" , "Like other crimes" .)