catachthonian [kætəkˈθəʊnɪan], a.
Etymology: f. Gr. καταχθόνιος subterranean, f. κατά down, under + χθόνιος of the ground, f. χθών ground + -ian.
Subterranean.
1888 Rhys Hibbert Lect. 131 - Pluto..was always..a chthonian or catachthonian Zeus.
So catachˈthonic a.
1884 Athenæum 8 Mar. 314/3 - In the Takashima coal-mine..an underground, or, as he prefers to call it, a catachthonic observatory.