Careless about slip (6)
I believe the answer is:
remiss
'careless' is the definition.
(thesaurus)
'about slip' is the wordplay.
'about' becomes 're' (regarding).
'slip' becomes 'miss' (**).
're'+'miss'='REMISS'
(Other definitions for remiss that I've seen before include "Not taking care" , "Culpable" , "Lacking attention to duty" , "Derelict in duty" , "Careless concerning a girl?" .)