properly speaking, the name of a lake in Campania, which the Latin poets describe as the entrance to the lower world, or as the lower world itself. Here we have only to mention, that Avernus was also regarded as a divine being; for Servius (ad Virg. Georg. 2.161) speaks of a statue of Avernus, which perspired during the storm after the union of the Avernian and Lucrinian lakes, and to which expiatory sacrifices were offered.
[L.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890