Other forms: planets
A planet is a huge round world circling a star. The planets, planet Earth, an outer planet.
The current definition requires it to orbit the sun, be round under its own gravity, and have cleared its orbital neighbourhood — the third condition is what demoted Pluto in 2006 and started an argument that has not stopped. The name means wanderer, because these were the lights that moved against the fixed stars. Note planetary; and that thousands of planets are now known around other stars.
1nounplanetA large round world circling a star.
“Mars is known as the red planet.”
planet is a celestial body.
Greek planetes means wanderer, from planasthai, to stray. The planets were named for moving against the fixed stars, which is what the ancient astronomers noticed first.
Ancient Greek
πλανήτης — wanderer
Latin
planeta
Old French
planete
Middle English
planete
English, today
planet
From Middle English planete, from Old French planete, from Latin planeta, planetes, from Ancient Greek πλανήτης (“wanderer”) (itself an an ellipsis of ἀστέρες πλανῆται), from Ancient Greek πλανάω (“wander about, stray”), of unknown origin. Cognate with Latin pālor (“wander about, stray”), Old Norse flana (“to rush about”), and Norwegian flanta (“to wander about”). More at flaunt. So called because they have apparent motion, unlike the "fixed" stars. Originally including also the moon and sun but not the Earth; modern scientific sense of "world that orbits a star" is from 1630s in English. The Greek word is an enlarged form of πλάνης (“who wanders around, wanderer”), also "wandering star, planet", in medicine "unstable temperature." Displaced native tungol.
Etymology from Wiktionary, CC BY-SA