Lethe
Λήθη
One sip, and everything you have lived is forgotten.
One of the five rivers of the underworld; a soul that drinks its water forgets its past life.
The final book of Plato's Republic has a scene in which every soul drinks this water before being born again.
The Greek word for truth, aletheia, literally means "the unhidden" — the opposite of Lethe.
SourcesPlato, Republic