Course change is reversed (4)
I believe the answer is:
tide
'course' is the definition.
(tiding is a kind of coursing)
'change is reversed' is the wordplay.
'change' becomes 'edit' (editing is a kind of changing).
'is reversed' says the letters should be written backwards.
'edit' written backwards gives 'TIDE'.
(Other definitions for tide that I've seen before include "One thing that waits for no man" , "What might carry" , "''There is a ... in the affairs of men'' (Julius Caesar)" , "Ebb and flow of the sea" , "Sea's ebb and flow" .)