Each of these words refers to persons or animals engaged in struggles or contests. Related words are opponent, competitor, and rival. An adversary is an opponent toward whom one does not necessarily feel animosity or hatred. An antagonist is a definitely hostile opponent."Counsel for the defense faced an experienced adversary in District Attorney Smythe." "A flyweight boxer is not a suitable antagonist for a middleweight."
Dictionary of problem words and expressions. Harry Shaw. 1975.