Source : Webster's Revised Unabridged Dictionary (1913)

Lethe \Le"the\ (l[=e]"th[-e] or l[=e]th), n. [See {Lethal}.]
   Death.[Obs.] --Shak.

Lethe \Le"the\ (l[=e]"th[-e]), n. [L., fr. Gr. lh`qh, prop.,
   forgetfulness; akin to lanqa`nesqai to forget, lanqa`nein to
   escape notice.]
   1. (Class. Myth.) A river of Hades whose waters when drunk
      caused forgetfulness of the past.

   2. Oblivion; a draught of oblivion; forgetfulness.

Source : WordNet®

Lethe
     n : (Greek mythology) a river in Hades; the souls of the dead
         had to drink from it, which made them forget all they had
         done and suffered when they were alive [syn: {River Lethe}]