Definitions

1. noun

A hypothetical celestial object that orbits a star but does not clear the neighborhood around its orbit, such as a large asteroid.

“The discovery of the new antiplanet suggested that our understanding of planetary formation was incomplete.”

2. noun

An object or entity that is the opposite or counterpart of a planet, often used in science fiction.

“In the sci-fi novel, the antiplanet was a dark mirror to the protagonist’s home planet.”