Cash returns for Jack, say (4)
I believe the answer is:
tool
'for jack say' is the definition.
(jack is a kind of tool)
'cash returns' is the wordplay.
'cash' becomes 'loot' (loot can mean stolen money).
'returns' says the letters should be written backwards.
'loot' written backwards gives 'TOOL'.
(Other definitions for tool that I've seen before include "Device used for work" , "one of 12 [SPADES] , for example" , "Person used by another" , "Cat's-paw; impress design on" , "Gun" .)