A king given a black horse (4)
I believe the answer is:
arab
'horse' is the definition.
(Arab is an example)
'a king given a black' is the wordplay.
'a king' becomes 'ar' (I've seen this in other clues**).
'given' says to put letters next to each other.
'black' becomes 'b' (as in pencil classifications).
'ar'+'a'+'b'='ARAB'
(Other definitions for arab that I've seen before include "Small riding horse" , "Qatari or Omani, say" , "Person from the Middle East, say" , "Native of North Africa" , "One from Saudi" .)