adversary n.反对者
rival n. 对手
区别
adversary暗含难以对付的对手，而且可能产生敌意
rival一般指参与竞赛的对手验
adversary=enemy意思是敌人，opponent意思是对手
查一下柯林斯词典：
opponent：a person who opposes another in a contest, battle, etc
enemy:a person hostile or opposed to a policy, cause, person, or group, esp one who actively tries to do damage
adversary:a person or group that is hostile to someone
可见，adversary=enemy是怀有仇恨的对手，既敌人。而opponent仅仅指代竞争或比赛中的对手而已。
