Casino tycoon puts down $1000 on horse (5)
I believe the answer is:
pacer
'horse' is the definition.
(a horse which paces)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pacer that I've seen before include "early race leader?" , "One who sets the running speed; horse" , "One walking steadily" , "Competitor" , "walker?" .)