Shoot the shearer (3)
I believe the answer is:
gun
'shoot' is the definition.
(gunning is a kind of shooting)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for gun that I've seen before include "Platform from which to shoot" , "Throttle" , "Hand weapon" , "Firearm" , "Hired killer" .)