Horse hastener (4)
I believe the answer is:
spur
(Other definitions for spur that I've seen before include "'Urge, goad (4)'" , "Goad - incentive" , "Provoke" , "offer encouragement" , "Impulse" .)
I believe the answer is:
spur
(Other definitions for spur that I've seen before include "'Urge, goad (4)'" , "Goad - incentive" , "Provoke" , "offer encouragement" , "Impulse" .)