Lewis & Short

Ăchĕrūsĭus (old writing Acherunsius), a, um, adj. [Acheruns].

  1. I. Pertaining to the Acheron in Calabria: aqua, Liv. 8, 24.
  2. II. Pertaining to the Acheruns (Acheron), or the Lower World: templa, the Lower World, Enn. ap. Cic. Tusc. 1, 21, 48 (Trag. v. 107 ed. Vahl.); in Varr. L. L. 7, § 6 Müll.; and in Lucr. 1, 120; cf. Lucr. 3, 25 and 86: humor, Sil. 13, 398: vita, a life of gloom, Lucr. 3, 1024.
  3. III. Pertaining to Acheron in Epirus: amnis, Just. 12, 2, 3.