chthonicadj.

chthonic (adj.)1882, with suffix -ic, from Greek khthonios "of the earth, in the earth," from khthon "the earth, solid surface of the earth" (mostly poetic) from PIE root *dhghem- (cognates: Greek khamai "on the ground," first element in chameleon; also Latin humus "earth, soil," humilis "low;" Lithuanian žeme, Old Church Slavonic zemlja "earth;" Sanskrit ksam- "earth" (opposed to "sky"); Old Irish du, genitive don "place," earlier "earth").