Corrupt practices a sailor employs (6)
I believe the answer is:
abuses
'corrupt practices' is the definition.
(I've seen this in another clue)
'a sailor employs' is the wordplay.
'a sailor' becomes 'ab' (abbreviation for able seaman).
'employs' becomes 'uses' ('use' can be a synonym of 'employ').
'ab'+'uses'='ABUSES'
(Other definitions for abuses that I've seen before include "Reviles or takes undue advantage." , "Reviles and insults" , "Maltreats people or things" , "Curses" , "Treats cruelly" .)