American English

Definition of planet noun from the Oxford Advanced American Dictionary



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  1. 1[countable] a large round object in space that moves around a star (such as the sun) and receives light from it the planets of our solar system the planet Earth/Venus/Mars
  2. 2the planet [singular] used to mean “the world,” especially when talking about the environment the battle to save the planet
  3. Idioms
    to be on another planet, what planet is somebody on? (informal) (humorous)
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    used to suggest that someone's ideas are not realistic or practical He thinks being a father is easy. What planet is he on?
See the Oxford Advanced Learner's Dictionary entry: planet