1. A hypothetical Earth which is counter to ours; counter Earth: An antichthon is on the opposite side of the sun.
2. Inhabitants of opposite hemispheres: Jill read about antichthons, an obsolete term for those dwellers of the antipodes.

In geography, the people who inhabit countries on opposite sides of the Earth: Back in the times of Medieval Europe, it was believed that the Earth was divided into the northern hemisphere and the southern Hemisphere, and those living in one of these two hemispheres considered those living in the other hemisphere to be antichthones.