Sudden shock (4)
I believe the answer is:
jolt
'sudden shock' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for jolt that I've seen before include "Jostle; shock" , "Sudden shock" , "Knock sharply so as to dislodge" , "Shock, jerk" , "elbow" .)