Cheat; instrument (6)
I believe the answer is:
fiddle
This clue is a double definition.
'cheat' is the first definition.
(I've seen this before)
'instrument' is the second definition.
(I know that fiddle is a type of bowed stringed instrument)
(Other definitions for fiddle that I've seen before include "do crookedly with books" , "Fix" , "Sham" , "Cook" , "doctor" .)