What does planetoid mean?
A planetoid is, in modern usage, a small celestial body that resembles a planet, especially an asteroid or minor planet. The word is broad and somewhat old-fashioned: scientific discussions often prefer more specific terms such as “asteroid,” “minor planet,” or “dwarf planet.” Its historical sense simply meant “a planet,” but that use is now rare and generally understood from older texts. The term can be useful when an author wants to discuss small bodies in the solar system without committing to a precise classification. Its form is also associated with the wider family of words derived from Greek roots meaning “wanderer,” including planet and planetary, reflecting the ancient observation that planets appear to move against the background of the stars.
nounA small celestial body, especially one orbiting the Sun, that is broadly similar to a planet; in modern astronomy, the term is often used broadly for minor planets and other small planetary bodies. In older usage, it was also an uncommon synonym for a planet.
- A small celestial body, especially an asteroid or minor planet, that is broadly similar to a planet.
- Archaically, a planet itself.
"The newly discovered planetoid travels through the outer region of the solar system."
"Astronomers tracked the planetoid as it passed close to Earth."
"In an old astronomy text, the author described Jupiter as a distant planetoid."
The standard plural is “planetoids.”
"Several planetoids were visible through the telescope."
Once, “planetoid” could be a grand name for any planet; today it more often describes the smaller bodies that populate the solar system.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does planetoid come from?
The word was formed in the 19th century from planet and the suffix -oid, meaning “resembling” or “like.” Its ultimate roots are Greek planētēs, a “wanderer,” and planētos, “wandering,” referring to the apparent movement of stars and planets. The same root also underlies planetary and planetesimal, while planet itself reflects the same ancient astronomical terminology.
Related word forms
How planetoid is actually used
The modern astronomical sense is uncommon in precise scientific writing, where terms such as “minor planet” or “asteroid” may be more appropriate. The older sense meaning “planet” is chiefly historical and literary.
Easily confused with planetoid
An asteroid is a specific type of small rocky body, whereas planetoid is a broader, sometimes archaic term that can refer to a small body more generally.
A dwarf planet is a body that has cleared its orbital neighbourhood and is not a satellite, while planetoid is a broader term and does not require that classification.