Galley mark (4)
I believe the answer is:
stet
'galley mark' 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 "Print as is, don't alter spelling" , "Let it stand (editing mark)" , "Don't alter, let spelling stand" , "Word to cancel change" , "cancel amendment" .)