Jerry's adversary
I believe the answer is:
tom
'jerry's adversary' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tom that I've seen before include "Jerry's cartoon antagonist" , "Cruise" , "Man's name; male cat" , "- Lehrer, US humorist" , "What Dick Whittington had" .)