Ruler of Qatar (4)
I believe the answer is:
emir
'ruler of qatar' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for emir that I've seen before include "Middle-Eastern ruler" , "Title of various rulers; I'm ER (anag.)" , "Title of various Muslim rulers" , "Top man" , "Arab leader" .)