Careless agent accepting cut (6)
I believe the answer is:
sloppy
'careless' is the definition.
(synonyms)
'agent accepting cut' is the wordplay.
'agent' becomes 'spy' (spy is a kind of agent).
'accepting' indicates putting letters inside (inserted letters are accepted).
'cut' becomes 'lop' (lopping is a kind of cutting).
'spy' placed around 'lop' is 'SLOPPY'.
(Other definitions for sloppy that I've seen before include "Runny" , "maudlin" , "Excessively casual" , "Slipshod" , "Lacking neatness and order" .)