From Longman Dictionary of Contemporary Englishplanetplan‧et /ˈplænɪt/ ●●● W3 noun [countable] 1 
HAa very large round object in space that moves around the Sun or another star Mercury is the smallest of all the planets. Is there life on other planets? the future of planet Earth ► Don’t say ‘in a planet’. Say on a planet.2 → somebody is (living) on another planet/what planet is somebody on?3 → the planet —planetary adjective [only before noun] the planetary system
HAa very large round object in space that moves around the Sun or another star Mercury is the smallest of all the planets. Is there life on other planets? the future of planet Earth ► Don’t say ‘in a planet’. Say on a planet.2 → somebody is (living) on another planet/what planet is somebody on?3 → the planet —planetary adjective [only before noun] the planetary systemExamples from the Corpus
planet• In this way the differentiation of a planet may act to slow down the operation of the heat engine.• One of my boyfriends said that it's as if I was from another planet.• We will take the animals to different planets.• The entire planet is fluid, like a star.• Certainly, evidence of intelligent civilizations on planets orbiting distant stars would be an epochal event in human history.• It is almost certain that, during the Earth's early history, the planet was a frequent victim of cometary impacts.• Saturn is the planet with rings around it.• The orbital motion of the earth provided a causal explanation for why the planets appeared to meander across the sky.Origin planet (1100-1200) Old French planete, from Late Latin planeta, from Greek planes “wanderer” 