Saying in a soft, indirect, or veiled way something harsh, ugly, or forbidden to name.
In Macbeth
We have scorched the snake, not killed it. [...] Better be with the dead, / Whom we, to gain our peace, have sent to peace, / Than on the torture of the mind to lie / In restless ecstasy.
The ones he and his wife killed are the ones they "sent to eternal peace." The phrase softens the word death, and the softness sounds bitter, because the king ends up envying those dead.