Remove a rotten cheat to a good end (6)
I believe the answer is:
detach
'remove' is the definition.
(I've seen this before)
'a rotten cheat to a good end' is the wordplay.
'a rotten' indicates an anagram.
'to' says to put letters next to each other (I've seen this in other clues).
'end' says to take the final letters.
The last letter of 'good' is 'd'.
'cheat' with letters rearranged gives 'etach'.
'etach' after 'd' is 'DETACH'.
(Other definitions for detach that I've seen before include "free" , "Remove from something else, say a coupon" , "Separate, disconnect" , "Remove from contact" , "Break off, come away" .)