1882, from Gk. khthonios "in the earth," from khthon "the earth, solid surface of the earth" (mostly poetic) from PIE root *dhghem- (cf. first element in chameleon, also L. humus "earth, soil," humilis "low;" Lith. zeme, O.C.S. zemlja "earth;" Skt. ksam- "earth" (opposed