Deal with enemy, ultimately making pact (6)
I believe the answer is:
treaty
'pact' is the definition.
('treaty' can be a synonym of 'pact')
'deal with enemy ultimately' is the wordplay.
'deal with' becomes 'treat' ('treat' can be a synonym of 'deal with').
'enemy ultimately' becomes 'y' (I am not sure about this - if you are sure you should believe this answer much more).
'treat'+'y'='TREATY'
'making' is the link.
Can you help me to learn more?
(Other definitions for treaty that I've seen before include "Compact; concordat" , "Yatter (anag.)" , "Political or private agreement" , "Negotiation" , "Compact - agreement" .)