Whig's rival
I believe the answer is:
tory
'whig's rival' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tory that I've seen before include "Traditionalist" , "blue" , "Politician; tyro (anag.)" , "English Conservative politician or Donegal island" , "Opponent of 8 Down and 14 Across, partner of 14 Down?" .)