the state of something that has outlived its relevance
mail that can neither be delivered nor returned
dead letter的用法和样例:
例句
用作名词 (n.)
The name of the exception class for the player to activate and play back before the message is routed to the dead letter queue. 用于在消息被路由到死信队列之前由播放机激活并播放的异常类的名称。