Answer: lethes

AnswerCrossword Clue
LETHES... waters caused forgetfulness.
LETHESStates of oblivion
lethesLETHE, forgetfulness
lethesforgetfulness; oblivion
lethesriver in Hades whose water caused forgetfulness of the past in those who drank of it
lethesa river in Hades whose waters cause drinkers to forget their past