Slur (6)
I believe the answer is:
insult
'slur' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for insult that I've seen before include "Treat with contempt" , "Abuse (someone)" , "Hurtful and offensive remark" , "Speak or act in way designed to hurt" , "Slight - affront" .)