Achilles adversary (5)
I believe the answer is:
paris
'achilles adversary' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for paris that I've seen before include "Prince who abducted Helen, starting a long war (see 8)" , "captivated Helen" , "City on the Seine" , "where he got plastered?" , "English chronicler" .)