Definition from Wiktionary, the free dictionary
chthonian (not comparable)
- Pertaining to the underworld; being beneath the earth.
- 1955: ...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. — W.K.C. Guthrie, The Greeks and Their Gods (Beacon Press 1955, p. 219)