Leader; most important (5)
I believe the answer is:
chief
I believe this is a double definition.
'leader' is the first definition.
(I know that chief is a type of leader)
'most important' is the second definition.
(I've seen this in another clue)
(Other definitions for chief that I've seen before include "arch" , "Person in charge, head" , "Tribal leader" , "Organisation head" , "Principal" .)