A mistake of supervision (9)
I believe the answer is:
oversight
I believe this is a double definition.
'a mistake' is the first definition.
(I know that oversight is a type of mistake)
'supervision' is the second definition.
(I know that supervision can be written as oversight)
'of' acts as a link.
(Other definitions for oversight that I've seen before include "Management" , "Shot giver due to unintentional omission" , "Supervisor's charged with this" , "act of negligence" , "error" .)