Opponent (4)
'opponent' is the definition.
(a rival is an opponent or enemy)
This is all the clue.
(Other definitions for rival that I've seen before include "Close competitor" , "Competing opponent" , "Adversary, antagonist" , "Contender" , "Challenger, competitor" .)
'opponent' is the definition.
(I know that enemy is a type of opponent)
This is all the clue.
(Other definitions for enemy that I've seen before include "Time" , "Division" , "Yemen (anag.)" , "one in opposition" , "Rival" .)
'opponent' is the definition.
(I know that foe is a type of opponent)
This is all the clue.
(Other definitions for foe that I've seen before include "opposing side" , "Someone opposing" , "Opponent" , "Am archaic enemy" , "Adversary" .)
'opponent' is the definition.
(synonyms)
This is all the clue.
(Other definitions for adversary that I've seen before include "Opponent or enemy" , "Foe, opponent" , "Antagonist, opponent" , "Enemy or rival" .)
'opponent' is the definition.
(someone opposed to something)
This is the entire clue.
(Other definitions for anti that I've seen before include "Prefix meaniing against" , "not favoured" , "Adversary" , "Someone opposed (to a policy?)" , "Definitely not pro" .)