Killing of one's mother (9)
I believe the answer is:
matricide
'killing of one's mother' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for matricide that I've seen before include "Killer" , "Murder of one's mother" , "Murderer" , "The killing of one's mother" , "Diametric killing of a mother" .)