Attack messages from the east (3,2)
I believe the answer is:
set on
'attack' is the definition.
(synonyms)
'messages from the east' is the wordplay.
'messages' becomes 'notes' (note is a kind of message).
'from the east' shows that the letters should be reversed in order (on a map from right to left).
'notes' back-to-front is 'SET ON'.
(Other definitions for set on that I've seen before include "Determined" , "Go" , "Attack" .)