'acherontical' originates from Greek, specifically the word 'Acheron,' which is a river in Greek mythology associated with the underworld.

'Acheron' was adopted into Latin as 'Acheron,' and eventually became the English adjective 'acherontical' to describe something hellish or infernal.

Initially, it referred to the river Acheron itself, but over time it evolved to describe anything infernal or hellish.