Lapse in supervision (9)
I believe the answer is:
oversight
This clue is a double definition.
'lapse' is the first definition.
('oversight' can be a synonym of 'lapse')
'supervision' is the second definition.
('oversight' can be a synonym of 'supervision')
'in' is the link.
(Other definitions for oversight that I've seen before include "Lapse" , "Innocent mistake" , "what supervisor has" , "Neglect" , "Failure to notice something" .)