In King Lear, the phrase "If our father would sleep till I waked him" is used in Edmund's fake letter to Gloucester. Apparently it means "if our father were dead". What is the origin of the phrase? Why does "sleep till I waked him" mean dead?
The phrase occurs both in the 1608 quarto The History of King Lear and the 1623 First Folio, where the play's title is The Tragedy of King Lear. This can be seen in e.g. King Lear: A Parallel Text Edition. Second edition. Edited by René Weis. Harlow: Pearson Education, 2010.
René Weis adds the following annotation: "Edmund would not wake his father from sleep, i.e. 'If our father were dead'."
In the New Penguin Shakespeare, G. K. Hunter adds the following annotation: "if our father were put into my power to decide his sleeping or waking (that is, death or life)."
The association of sleep and death is not unusual in Shakespeare; it also occurs in Hamlet's "to be or not to be" soliloquy:
To die, to sleep –
No more; and by a sleep to say we end
The heartache and the thousand natural shocks (...)
(...): to die, to sleep.
To sleep, perchance to dream. (...)
In the Oxford Shakespeare edition of Hamlet, editor G. R. Hibbard comments on the fist line: "i.e. dying is no more than sleeping."
The association predates Shakespeare. See for example "The Parson's Tale" in Geoffrey Chaucer's The Canterbury Tales (quoted from The Riverside Chaucer page 292, emphasis added):
The riche folk, that embraceden and oneden al hire herte to tresor of this world, shul slepe in the slepynge of death; (...).
("oneden" means "united".)
The origin of the association between sleep and death in Western culture is probably biblical. See for example Daniel 12:2 (emphasis added):
And many of those who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt.
See also the concept of soul sleep to refer to the time between physical death and resurrection.
It cannot be that "wake" refers to the noun we today define as "a gathering of people to pay respects to a dead person who is laid out in their presence." Why? Because it would make nonsense, then, of the word "sleep." Why would someone necessarily have to be waked here (as in the noun sense I have just offered)? If Edmund wants his father Gloucester dead, then he is saying simply, "If we can imagine a scenario in which my father would go to sleep and stay asleep forever, unless or until I wake him up, then that sleep would be his death, for I would NEVER wake him up. I'd like not to have to actually kill him with my own hands, but if he could go to sleep and stay asleep and wake up only when I made him wake up (as if by some magic power I might be imagined to have) then that sleep would be his death, for I would never end it by waking him."
So "sleep until I laid him out for others to pay their respects at a wake" makes no sense here. If Edmund is saying he would end Gloucester's sleep by laying Gloucester out in a casket for others to pay their respects, he is not telling us by what means Gloucester would be made to change from sleeping to being dead. Obviously, we cannot "wake" a living person (again, "wake" used here as "the ceremony of laying out a dead person . . . ), so he could not be saying that Gloucester would just go on sleeping during his own wake!