Lady Macbeth (Shakespeare’s play “Macbeth,” Act V, Scene 1) is overwhelmed by a fearful sense of guilt because of the heinous crimes she had emboldened Macbeth to commit: regicide (the killing of King Duncan); the killing of Banquo; the murder of Lady Macduff and her family.
The literal translation would be: “Nothing could ever cover up this evil.” or “No euphemisms can hide the ugly reality.” This famous quote -- a metaphoric-hyperbolic phrase -- is uttered by Lady Macbeth as her conscience is being tormented by the knowledge of the crimes she and her husband did for power. Her doctor and lady in waiting are powerless; the doctor states that he cannot cure Lady Macbeth as she needs divine intervention, not medicine, for healing. (N.B. Some superstitions in Europe -- e.g. Scandinavian/Germanic sagas -- revived by mediaeval playwrights and, later, the Romantic Era -- indicate that the blood of an innocent victim cannot be washed away until the murdered one has been vindicated.) Lady Macbeth “sees” or “smells” Duncan's blood on her hands and – despite her criminal character – she is experiencing insidious fears about the imminent revenge of the victims.