Negligent misers reformed (6)
I believe the answer is:
remiss
'negligent' is the definition.
(similar in meaning)
'misers reformed' is the wordplay.
'reformed' is an anagram indicator.
'misers' with letters rearranged gives 'REMISS'.
(Other definitions for remiss that I've seen before include "Derelict in duty" , "Failing in what duty requires" , "Negligent, lax" , "Failing in one's duty" , "Careless and inattentive" .)