Deviate off course (3)
I believe the answer is:
yaw
'deviate off course' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yaw that I've seen before include "(Of ship) twist sideways" , "Ship's deviation" , "Go off course" , "Twisting motion (of ship)" , "Temporarily get off course" .)