Missing notes dispatched (6)
I believe the answer is:
absent
'missing' is the definition.
(similar in meaning)
'notes dispatched' is the wordplay.
'notes' becomes 'ab'.
'dispatched' becomes 'sent' (I've seen this before).
'ab'+'sent'='ABSENT'
(Other definitions for absent that I've seen before include "Not present - vacuous" , "AWOL" , "lack of attention" , "Missing or dreamy" , "Not present or focused" .)