Incentive for a horse? (4)
I believe the answer is:
spur
'incentive' is the definition.
(an incentive spurs someone on)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for spur that I've seen before include "Sharply pointed projection" , "Sharp pointed projection" , "Goad - incentive" , "Strong incentive" , "Encourage" .)