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

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

"El Niño is being supersized before our eyes. The science leaves no room for doubt: the planet is in uncharted waters, and those waters are heating up," Guterres said.

From BBC ● Sep. 3, 2026

"Nothing has changed in Italy over the 45 years I've been on this planet and nothing will," said Maurizio, a sandal-wearing IT worker who preferred to give only his first name.

From Barron's ● Sep. 2, 2026

“What good is defending the historic homeland of our ancestors and demanding that candidates acknowledge its right to exist, if the planet upon which it rests is no longer inhabitable?”

From The Wall Street Journal ● Sep. 2, 2026

As I unthreaded the tiny screws from the density buffer—whatever that was—I asked Klawde if he missed his home planet.

From "Klawde: Evil Alien Warlord Cat" by Johnny Marciano and Emily Chenoweth

Hubble's long operational history has given astronomers an unusual ability to follow changes on planets and other astronomical objects over many years.

From Science Daily ● Sep. 3, 2026

That should allow astronomers to study enormous numbers of galaxies, stars, and planets in a fraction of the time previously required.

From Science Daily ● Aug. 31, 2026

The findings suggest that rocky planets, and possibly worlds with some of the ingredients associated with habitability, may have become possible much earlier in cosmic history than scientists previously expected.

From Science Daily ● Aug. 31, 2026

The Roman telescope is also expected to locate more planets beyond our solar system, some of which could hold life like our own.

From The Wall Street Journal ● Aug. 30, 2026

Danny picked up a book on space with color photos of planets and found a couch where he could read.

From "The Way to Rio Luna" by Zoraida Cordova

Related Words

• asteroid
• earth
• globe
• sphere
• world