Death Knell Meaning

(idiomatic, by extension) A sign or omen foretelling the death or destruction of something.

Example: The tolling of a bell announcing death.
1873, Thomas Hardy, A Pair of Blue Eyes, ch. 25:
  The sound was the stroke of a bell from the tower of East Endelstow Church. . . . The death-knell of an inhabitant of the eastern parish was being tolled.
1890, Ambrose Bierce, An Occurrence at Owl Creek Bridge, ch. 1:
  Its recurrence was regular, but as slow as the tolling of a death-knell.
1901, Upton Sinclair, King Midas, ch. 10:
  The thought was a death-knell to Helen's last hope.
2004, Jamie James, "The Rise of a Musical Superpower," Time, 28 June:
  "It is the death knell of an orchestra if it doesn't have its own home," he says.