κατα-χθόνιος, -ον (χθών, the earth), subterranean, under the earth (in cl., of the infernal gods): of the departed in Hades, opposite to ἐπουράνιος, ἐπίγειος, Php.2:10.† (AS)
STRONG'S WORD STUDY
G2709 — καταχθόνιος
katachthonios · subterranean · Greek