Notice the absence of failure (4)
I believe the answer is:
miss
This clue is a double definition.
'notice the absence of' is the first definition.
(I've seen this in another clue)
'failure' is the second definition.
(I know that miss is a type of failure)
(Other definitions for miss that I've seen before include "someone who isn't married" , "Girl or unmarried woman" , "Fail to hear" , "Fail to catch" , "Feel the absence of" .)