Rival pair (5)
I believe the answer is:
match
I believe this is a double definition.
'rival' is the first definition.
(synonyms)
'pair' is the second definition.
(synonyms)
(Other definitions for match that I've seen before include "Go together" , "Game - pairing - lucifer" , "Contest; pair" , "Stick in a box?" , "Sporting event" .)