Swerve off course (4)
I believe the answer is:
veer
'swerve off course' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for veer that I've seen before include "Swing around" , "Change direction or course, like wind" , "Swerve" , "Deviate" , "Sudden direction change" .)