Diss (6)
I believe the answer is:
insult
'diss' is the definition.
(I know that diss can be written as insult)
This is all the clue.
(Other definitions for insult that I've seen before include "Demeaning remark" , "Cause offence to" , "Treat with abuse" , "Treat disrespectfully" , "Hurtful and offensive remark" .)