One is a Muslim leader (4)
I believe the answer is:
imam
I believe this clue is a double definition.
'one is a muslim' is the first definition.
(I know that imam is a type of Muslim)
'leader' is the second definition.
(I know that imam is a type of leader)
(Other definitions for imam that I've seen before include "Islamic religious leader" , "Muslim community leader" , "Maim (anag)" , "Man who leads prayers in a mosque" , "Muslim holy man" .)