G2709 καταχθόνιος (katachthónios)

KJV renderings: under the earth
Strong's definition: subterranean, i.e. infernal (belonging to the world of departed spirits)
Derivation: from G2596 (κατά) and (the ground);

From James Strong's public-domain dictionaries (G), JSON edition by OpenScriptures (CC-BY-SA). Every dotted-underline word in the text links here.