Lewis & Short

Lēthē, ēs, f., = Λήθη (forgetfulness),

  1. I. the river Lethe, in the infernal regions, from which the Shades drank and obtained forgetfulness of the past: pocula Lethes, Ov. P. 2, 4, 23: da mihi hebetantem pectora Lethen, id. ib. 4, 1, 17: soporifera, id. Tr. 4, 1, 47: immittere Lethen Stygiam alicui in viscera, i. e. forgetfulness, Luc. 5, 221: aqua Lethes, i. q. soporifera, Ov. M. 11, 603.
    Hence,
  2. II. Lēthaeus, a, um, adj., of or belonging to Lethe, Lethean.
    1. A. Lit.: ratis, Tib. 3, 5, 24: amnis, Verg. A. 6, 705: stagna, Prop. 4 (5), 7, 91.
    2. B. Transf.
      1. 1. Of or belonging to the infernal regions: Lethaei dii, Luc. 6, 685: tyrannus, i. e. Pluto, Col. 10, 271: Lethaea vincula abrumpere alicui, to bring one from the Lower World back to life, Hor. C. 4, 7, 27: janitor, i. e. Anubis, Stat. S. 3, 2, 112.
      2. 2. That produces sleepiness or forgetfulness, Lethean: Lethaeo perfusa papavera somno, Verg. G. 1, 78: ros, id. A. 5, 854: papavera, id. G. 4, 545: sucus, Ov. M. 7, 152: amor, faithless love, id. R. Am. 551: nox, id. A. A. 3, 648.