Deal with English missile going west (5)
I believe the answer is:
trade
'deal with' is the definition.
(thesaurus)
'english missile going west' is the wordplay.
'english' becomes 'E' (abbreviation).
'missile' becomes 'dart' (Backwards).
'going west' says the letters should be written in reverse (letters heading to the west or left).
'e'+'dart'='edart'
'edart' back-to-front is 'TRADE'.
(Other definitions for trade that I've seen before include "Commerce - traffic" , "Commercial exchange of goods and services" , "Buy and sell in business" , "Give and receive (blows)" , "Buying/selling of goods" .)