Aim to kill (3)
I believe the answer is:
end
This clue is a double definition.
'aim' is the first definition.
(both can mean a goal or purpose)
'kill' is the second definition.
(I've seen this in other clues)
'to' acts as a link.
(Other definitions for end that I've seen before include "Aim; terminate" , "Aim - point - finish" , "Conclude" , "Closure" , "Novel by Graham Greene" .)