aver·nal \əˈvərnəl\adjective oraver·ni·an\-nēən, -nyən\ Usage: sometimes capitalized Etymology:avernal from Latin Avernalis of Avernus, from Avernus, lake near Pozzuoli, Italy (now Lago Averno), reputed because of its depth and stench to lead to the underworld, underworld + Latin -alis -al; avernian from Avernus + English -ian : infernal