facilis descensus
/ˈfasɪlɪs dɛˈsɛnsəs/ /ˈfakɪlɪs dɛˈskɛnsəs/noun
With reference to Virgil's use: ‘easiness of the descent’ or an easy descent; especially the easiness and rapidity of moral decline or falling into bad ways; (also) the way to ruin, the ‘downhill slope’; an instance of this. See facilis descensus Averni.
Origin
Early 19th century; earliest use found in Edinburgh Magazine & Literary Miscellany. Short for facilis descensus Averni.