Cheat’s tool (6)
I believe the answer is:
chisel
This clue is a double definition.
'cheat's' is the first definition.
(I've seen this before)
'tool' is the second definition.
(chisel is a kind of tool)
(Other definitions for chisel that I've seen before include "Sharp-edged metal tool" , "Wood, stone or metal-cutting tool" , "Carpenter's or mason's tool" , "Cutting tool used with hammer" , "Tool used to shape wood, stone or metal" .)