Ruler from east, on edge going west (4)
I believe the answer is:
emir
'ruler' is the definition.
(emir is a kind of ruler)
'east on edge going west' is the wordplay.
'east' becomes 'e' ('E' can be a synonym of 'east').
'on' says to put letters next to each other.
'edge' becomes 'rim' (rim is a kind of edge).
'going west' says the letters should be written in reverse.
'rim' backwards is 'mir'.
'e'+'mir'='EMIR'
'from' acts as a link.
(Other definitions for emir that I've seen before include "Islamic ruler" , "Leading role" , "Title of various rulers; I'm ER (anag.)" , "Arab leader" , "leader in the East" .)