dead letter

名词（无法投递的）死信，形同虚设的规定

1. 形同虚设的法律（或协议）；空文
    If you say that a law or agreement is a dead letter, you mean that it still exists but people ignore it.

    e.g. No one does anything about it and the law becomes a dead letter.
           没有人执行它，该法律变成了一纸空文。

1. A woman has received a letter from a financial recovery firm claiming that she is dead.

noun