Unintentional omission (9)
I believe the answer is:
oversight
'unintentional omission' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for oversight that I've seen before include "Shot giver due to unintentional omission" , "Mistake resulting from inattention" , "what supervisor has" , "Supervision - omission" , "error" .)