Lean to one side (4)
I believe the answer is:
tilt
'lean to one side' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tilt that I've seen before include "Slope; joust" , "Cause to slope or incline" , "Stab" , "Incline, lean" , "Slope; use a lance in jousting" .)