Westward course is correct (4)
I believe the answer is:
edit
'is correct' is the definition.
(edit can mean to correct or emend)
'westward course' is the wordplay.
'westward' says the letters should be written backwards.
'course' becomes 'tide' (tiding is a kind of coursing).
'tide' backwards is 'EDIT'.
(Other definitions for edit that I've seen before include "Literally, arrange" , "Make alterations (in text)" , "Amend and correct" , "Check text for publication" , "Adjust text" .)