Title of rulers in some Asian countries (4)
I believe the answer is:
khan
'title of rulers in some asian countries' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for khan that I've seen before include "Central Asian prince or chief" , "Title given to rulers in Asian countries" , "Caravanserai; Asian ruler" , "Eastern potentate" , "Title of respect in central Asia (for a descendant of Genghis?)" .)