death knell
noun
in sing.
1- the tolling of a bell to mark someone's death丧钟声。
1.1
- figurative an event that heralds the end or destruction of something〈喻〉丧钟, 完结的信号：
the chaos may sound the death knell for the peace plan.
混乱可能敲响和平计划的丧钟。