death bell

WordReference Random House Unabridged Dictionary of American English © 2025

death′ bell′, 

1. the bell that announces a death.

• 1730–40

WordReference Random House Unabridged Dictionary of American English © 2025

death′ knell′, 

1. a harbinger of the end, death, or destruction of something.
2. See passing bell. 

Collins Concise English Dictionary © HarperCollins Publishers::

death knell, death bell noun

1. something that heralds death or destruction
2. a bell rung to announce a death