chthonian

[thoh-nee-uh n] /ˈθoʊ ni ən/
adjective, Classical Mythology
1.
of or pertaining to the deities, spirits, and other beings dwelling under the earth.
Also, chthonic
[thon-ik] /ˈθɒn ɪk/ (Show IPA)
.
Origin
1840-50; < Greek chthóni(os) (chthon-, stem of chthṓn earth + -ios adj. suffix) + -an; akin to Latin humus earth (see humus)
British Dictionary definitions for chthonian

chthonian

/ˈθəʊnɪən/
adjective
1.
of or relating to the underworld
Word Origin
C19: from Greek khthonios in or under the earth, from khthōn earth
Word Origin and History for chthonian
adj.

1804, from Latinized form of Greek khthonios (see chthonic) + -an.