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 to "sky"); O.Ir.
du, gen.
don "place," earlier "earth").
Chthonian is from 1850.