Many a Mauritanian (4)
I believe the answer is:
arab
'many a mauritanian' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for arab that I've seen before include "Horse of a breed originating in the Middle East" , "Mount" , "One from the Middle East or North Africa" , "Semite" , "Small riding horse" .)