End of a motorway going west (3)
I believe the answer is:
aim
'end' is the definition.
(both can mean a purpose or goal)
'a motorway going west' is the wordplay.
'motorway' becomes 'MI' (resembles M1, English motorway).
'going west' says the letters should be written in reverse (letters heading to the west or left).
'mi' back-to-front is 'im'.
'a'+'im'='AIM'
'of' acts as a link.
(Other definitions for aim that I've seen before include "mission" , "Purpose in directing the rifle" , "This is mean" , "Ambition or goal" , "Point (a camera)" .)