counterearth

[ koun-ter-urth ]
/ ˈkaʊn tərˌɜrθ /

noun

(in Pythagorean astronomy) a planet, out of sight from our part of the earth, whose shadow upon the sun and moon, cast by a central fire that is also out of sight, causes the eclipses.

Origin of counterearth

1855–60; counter- + earth, as translation of Greek antíchthōn
Also called antichthon.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019