1580s, fabled river of the Lower World in Greek mythology, from Greek Akheron, name of several real rivers, also the mythical river of the Underworld. The name perhaps means "forming lakes" (compare Greek akherousai "marsh-like water"), from PIE root *eghero- "lake" (source of Lithuanian ežeras, ažeras, Old Prussian assaran, Old Church Slavonic jezero "lake"). The derivation from Greek akhos "woe" is considered folk etymology. The name was later given to rivers in Greece and Italy that flowed through dismal surroundings or disappeared underground. Related: Acherontic.