Deviate from route northwards (3)
I believe the answer is:
yaw
'deviate' is the definition.
(I know that yaw is a more specific form of the action deviate)
'route northwards' is the wordplay.
'route' becomes 'way' (way is a kind of route).
'northwards' is a reversal indicator (in a down clue, letters go up or 'north').
'way' back-to-front is 'YAW'.
'from' is the link.
(Other definitions for yaw that I've seen before include "Ship's deviation" , "Deviation (of e.g. ship)" , "Go off course" , "Twisting motion (of ship)" , "Temporarily get off course" .)