Speedy steed (4)
I believe the answer is:
arab
'speedy steed' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arab that I've seen before include "Small, lively breed of horse" , "Person from the Middle East, say" , "Saudi, perhaps - breed of horse" , "Mount" , "Saudi, e.g." .)