chthonian UK /ˈkθəʊnɪən/US /ˈkθoʊni.ən/adjective 1noun 1forms 3 adjective1 •Pertaining to the underworld; being beneath the earth....I intend to apply the name chthonian to all gods and spirits of the earth, whether their functions are concerned with agriculture or with the grave and the world beyond, or (as often) with both. — 1950 noun1 •A dweller in the mythical underworld. formschthonians · more chthonian · most chthonian