这些名词均有“对手，敌手”之意。
opponent : 最常用词，通常指在争论、辩论、竞选或竞赛以及其它各种矛盾冲突中站在对立面的“对手”或“敌手”。
- a political opponent
政敌 - Leading opponents of the proposed cuts in defence spending will meet later today.
反对削减国防开支建议的带头人将在今天晚些时候会面。 - In the second game, her opponent hurt her leg and had to retire.
在第二局，她的对手拉伤了腿，不得不退出比赛。
competitor : 指为同一目标或目的竞争者，一般无感情色彩。
- Their prices are better than any of their competitors.
他们的价格比所有竞争对手的都要优惠。 - How many competitors took part in the race?
有多少选手参加了赛跑？
enemy : 多指充满敌意的仇敌。
- He’s made a few enemies in this company.
他在公司中和几个人结了怨。 - Max stole Lee’s girlfriend and they’ve been enemies ever since.
马克斯抢走了李的女朋友，从那以后他们就成了冤家对头。 - political enemies
政敌 - The enemy had succeeded in stopping our supplies from getting through.
敌人成功切断了我军的补给线。 - an attack by enemy aircraft
敌机的空袭 - enemy forces/territory
敌军／敌区
foe : 语气较强，多用于书面文字和诗歌中。指不仅敌对，而且很危险，怀有很深的敌意。
- The two countries have united against their common foe.
两国联合起来对抗共同的敌人。 - They were bitter foes for many years.
他们结仇多年。 - Foes of the government will be delighting in its current difficulties.
政府的敌人会对政府目前的困难处境幸灾乐祸。
rival : 指与某人目标一致而想赶上或超过他的人，匹敌者。
- He beat his closest/nearest rival by 20 marks.
他以领先20分的成绩打败了和他水平最接近的对手。 - The companies produce rival versions of the toy.
这些公司生产的玩具跟我们的产品争夺市场。