Л-68

КАНУТЬ В ЛЁТУ (В РЕКУ ЗАБВЕНИЯ) lit VP subj: abstr or human fixed WO

to disappear completely, be forgotten forever

X канул в Лету X was swallowed up by Lethe (in the river of oblivion)

X sank into oblivion.

«Так, понимаете, и слухи о капитане Копейкине канули в реку забвения, в какую-нибудь эдакую Лету, как называют поэты» (Гоголь 3). "It was thus, you understand, that the rumours about Captain Kopeikin were swallowed up in the river of oblivion, in this-er-Lethe, as the poets call if (3a).

From Lethe («Лета»), the name of a river in Hades. In classical mythology, those who drank the water of Lethe-also called "the river of oblivion" («река забвения») - forgot the past.