a person or thing that is used to hide the real purpose of a particular course of action 用以掩人耳目的人（或物）；用以掩蔽的事物 a politician who competes against the leader of their party in order to see how much support the leader has; a stronger candidate can then compete against the leader more seriously （为试探对手支持率而推出的）掩护性候选人
Word Originearly 16th cent.: from the former practice of using a horse trained to allow a fowler (hunter of wildfowl) to hide behind it, or under its coverings, until within easy range of prey.