If you drink from the River Lethe in the underworld, you forget everything.
Someone wrote "No, no, go not to Lethe, neither twist / Wolf's bane ..for its poisonous wine." OK. Keats Ode to Melancholy.
p@ may well accuse me of showing off. Guilty.
sorry tombola, I don't have the xword today. Lethean comes from the word Lethe (a river of the underworld, causing forgetfulness to those who drank from it !)