noun 1A celestial body moving in an elliptical orbit round a star. Example sentences Kepler showed that a planet moves round the Sun in an elliptical orbit which has the Sun in one of its two foci. Nasa astronomers said they had found the smallest planets yet orbiting stars beyond our Sun. The planets all orbit the Sun in the same direction, with orbital planes inclined slightly to the ecliptic. Get more examples 1.1 (the planet) The earth: no generation has the right to pollute the planet More example sentences The high tax on petrol was put on in the first place to encourage people to use less of something which is polluting the planet. Ten years ago at the Rio earth summit the world accepted the need to manage the planet as a single whole for the whole of the human race. The idea behind the relay is to unite the world and infuse the planet with the Olympic spirit. Get more examples

The planets of the solar system are either gas giantsJupiter, Saturn, Uranus, and Neptuneor smaller rocky bodiesMercury, Venus, Earth, and Mars. Pluto, formerly regarded as the ninth planet, was in 2006 reclassified as a dwarf planet. The minor planets, or asteroids, orbit mainly between the orbits of Mars and Jupiter. Only Earth and Venus have substantial atmospheres

Middle English: from Old French planete, from late Latin planeta, planetes, from Greek plants 'wanderer, planet', from planan 'wander'.

Early Greek astronomers observed certain heavenly bodies moving around the night sky in contrast to the stars, which stayed permanently in a fixed position in relation to one another. This is why they are called planets, from Greek plants wanderer. The Sun and the Moon were once thought of as planets too. Plankton, the term for small and microscopic organisms floating in the sea, comes via German from the related Greek word planktos, wandering or drifting. See also aeroplane

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planet - definition of planet in English from the Oxford ...