Misers can be so careless (6)
I believe the answer is:
remiss
'careless' is the definition.
(I know that careless can be written as remiss)
'misers can be' is the wordplay.
'can be' indicates anagramming the letters.
'misers' is an anagram of 'REMISS'.
'so' acts as a link.
(Other definitions for remiss that I've seen before include "delinquent" , "Negligent in performance of duty" , "Failing in what duty requires" , "Negligent, lax" , "Negligent like misers" .)