Non-attendance (7)
I believe the answer is:
absence
'non-attendance' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for absence that I've seen before include "Cause of fonder heart?" , "Non-presence" , "Need" , "form of inattention?" , "''. . . . . . . makes the heart grow fonder'' (7)" .)