IDIOMS

big sleep

(idiomatic, euphemistic, almost always preceded by the) Death. [from 20th c.]

Example: 1939, Raymond Chandler, The Big Sleep, Penguin 2011, p. 250:
  What did it matter where you lay once you were dead? In a dirty sump or in a marble tower on top of a high hill? You were dead, you were sleeping the big sleep, you were not bothered by things like that.