Whigs' rivals (6)
I believe the answer is:
tories
'whigs' rivals' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tories that I've seen before include "Old British Conservatives" , "Right-wingers" , "The Right Stuff" , "Informal members of Conservative party in England" , "Members of the English Conservative Party" .)