Undo a dele (4)
I believe the answer is:
stet
'undo a dele' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stet that I've seen before include "Editing instruction that matter marked for deletion is to be retained" , "It may stand" , "Let it stand (L)" , "Instruction to leave spelling as is" , "Instruction to keep" .)