counterearth

[ koun-ter-urth ]

noun

1. (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.

Word History and Origins

Origin of counterearth¹

1855–60; counter- + earth, as translation of Greek antíchthōn