planet

American  

[plan-it] / ˈplæn ɪt /

noun

• planets
  plural

1. Astronomy.

   1. Also called major planet.  any of the eight large heavenly bodies revolving about the sun and shining by reflected light: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, or Neptune, in the order of their proximity to the sun. Until 2006, Pluto was classified as a planet ninth in order from the sun; it has been reclassified as a dwarf planet.

   2. a similar body revolving about a star other than the sun.

   3. (formerly) a celestial body moving in the sky, as distinguished from a fixed star, applied also to the sun and moon.

2. Astrology. the sun, moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto: considered sources of energy or consciousness in the interpretation of horoscopes.

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planet British  

/ ˈplænɪt /

noun

1. Also called: major planet.  any of the eight celestial bodies, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, that revolve around the sun in elliptical orbits and are illuminated by light from the sun

2. Also called: extrasolar planet.  any other celestial body revolving around a star, illuminated by light from that star

3. astrology any of the planets of the solar system, excluding the earth but including the sun and moon, each thought to rule one or sometimes two signs of the zodiac See also house

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planet Scientific  

/ plăn′ĭt /

1. In the traditional model of solar systems, a celestial body larger than an asteroid or comet, illuminated by light from a star, such as the Sun, around which it revolves.

2. A celestial body that orbits the Sun, has sufficient mass to assume nearly a round shape, clears out dust and debris from the neighborhood around its orbit, and is not a satellite of another planet. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was considered to be a planet until its reclassification in 2006 as a dwarf planet. A planetlike body with more than about ten times the mass of Jupiter would be considered a brown dwarf rather than a planet.

3. See also extrasolar planet inner planet outer planet

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planet Cultural  

1. An object in orbit around a star. A planet does not give off its own light; rather, it shines by reflecting sunlight. Planets close to the sun are rocky. Those farther out consist mostly of gas es and liquids.

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Discover More

There are nine major planets, including the Earth, in orbit around our sun, along with many asteroids. (See solar system.)

Scientists have discovered evidence for the existence of many planets that circle other stars.

Other Word Forms

Noun Inflected Forms

• planets
  plural

Etymology

Origin of planet

1250–1300; Middle English planete (< Old French planète ) < Late Latin planēta, planētēs (found only in plural planētae ) < Greek ( astéres ) planḗtai literally, wandering (stars)

Explanation

A planet is a celestial body that revolves around a star. In our solar system, Earth is the third planet from the sun. The word planet comes from the Greek planetes, which means "wanderer." Since ancient times, people have been fascinated by the wandering of celestial bodies in the night sky. If a variety of factors come together so that something works out well for you, you can say that the planets aligned. You parents weren't sure if your family was going to be able to go on vacation, but then the planets aligned and off to Florida you were.

Example Sentences

See Examples For:

planet planets

"I always thought that my dad's legacy is wildlife conservation; it turns out, his legacy is love. For our planet and for each other," Bindi, 28, wrote on Instagram.

From BBC ● Sep. 4, 2026

"They are therefore never neutral; when they present a distorted image of our planet, they risk perpetuating inaccurate representation that is passed down through generations."

From Barron's ● Sep. 4, 2026

In 2099, artificial intelligence has taken over the planet.

From Salon ● Sep. 4, 2026

Mars is commonly classified as a "stagnant lid" planet because, unlike Earth, its outer shell is not divided into moving tectonic plates.

From Science Daily ● Sep. 4, 2026

His Arctic expedition had begun successfully, even as the Advance sailed some of the most treacherous waters on the planet.

From "American Spirits" by Barb Rosenstock

The Mars findings suggest that complex crustal evolution and extensive geological recycling may be possible even on planets without Earth-style tectonics.

From Science Daily ● Sep. 4, 2026

Directly imaging such planets is extraordinarily difficult because a host star can be billions of times brighter than the planet orbiting it.

From Science Daily ● Aug. 31, 2026

The ingredients needed to build rocky planets may have appeared as early as 100 million years after the Big Bang, according to new research from the University of Portsmouth.

From Science Daily ● Aug. 31, 2026

The Coronagraph Instrument will demonstrate technology that could eventually be used by future missions such as NASA's Habitable Worlds Observatory concept to directly photograph planets resembling Earth.

From Science Daily ● Aug. 31, 2026

Taken all together, the moving planets made a “harmony of the spheres,” and the heavens are a beautiful mathematical orchestra.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife

Related Words

• asteroid
• earth
• globe
• sphere
• world