In classical mythology, a river flowing through Hades. The souls of the dead were forced to drink of its waters, which made them forget what they had done, said, and suffered when they were alive.
1567, river of Hades, whose water when drunk caused forgetfulness of the past, from Gk. lethe, lit. "forgetfulness, oblivion," related to lethargos "forgetful," lathre "secretly, by stealth," lathrios "stealthy," lanthanein "to be hidden." Cognate with L. latere "to be hidden" (see latent).