Misers sadly negligent (6)
I believe the answer is:
remiss
'negligent' is the definition.
(similar in meaning)
'misers sadly' is the wordplay.
'sadly' indicates anagramming the letters.
'misers' anagrammed gives 'REMISS'.
(Other definitions for remiss that I've seen before include "Negligent like misers" , "Failing in what duty requires" , "Negligent, derelict" , "Neglectful" , "Culpable" .)