• КАНУТЬ В ЛЕТУ (в РЕКУ ЗАБВЕНИЯ obs) 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 it" (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.
Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. С.И. Лубенская. 2004.