knell:1

noun
knell \ ˈnel \
before 12th century{ds||1||}
  • a stroke or sound of a bell especially when rung slowly (as for a death, funeral, or disaster)
  • an indication of the end or the failure of something

knell:2

verb
knell \
14th century{ds|i|1||}
  • to summon or announce by or as if by a knell
  • to ring especially for a death, funeral, or disaster : toll
  • to sound in an ominous manner or with an ominous effect

sound/ring/toll the death knell

idiom
sound/ring/toll the death knell \
  • to cause the end of
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