knell 
/ˈnɛl/ noun
plural knells /ˈnɛl/ noun [count] literary : a sound of a bell when it is rung slowly because someone has died ◊A death knell is a sign or indication that something will fail or end soon.
▪ The mistake was the death knell for his campaign. ▪ Many people thought that the Internet would sound/ring/toll the death knell for newspapers. [=cause the end of newspapers]
▪ The mistake was the death knell for his campaign. ▪ Many people thought that the Internet would sound/ring/toll the death knell for newspapers. [=cause the end of newspapers]
