plan ‧ et W3 /ˈplænət, ˈplænɪt/ BrE AmE noun [countable]
[ Date: 1100-1200 ; Language: Old French ; Origin: planete , from Late Latin planeta , from Greek planes 'wanderer' ]
1 . a 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
► Do not say ‘in a planet’. Say on a planet.
2 . somebody is (living) on another planet/what planet is somebody on? spoken used humorously to say that someone’s ideas are not at all practical or sensible:
He thinks motherhood is glamorous – what planet is he on?
3 . the planet the world – used especially when talking about the environment:
a safer future for the planet
—planetary adjective [only before noun] :
the planetary system
• • •
THESAURUS
■ in the sky
▪ star a large ball of burning gas in space, which can be seen at night as a point of light in the sky:
The dark night sky was clear and full of stars.
▪ planet one of the large objects that goes around the sun, for example the Earth, Saturn, Mercury, or Mars:
The planet Uranus was discovered in 1781.
▪ sun the star that gives us light and heat, around which the planets move. There are also many millions of other suns in the universe:
The sun came out from behind a cloud.
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a dying sun
▪ moon the round object that moves around the Earth every 28 days, or a similar object that goes around another planet:
The moon rose in the night sky.
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Titan is one of the moons of Saturn.
▪ asteroid a mass of rock that moves around the sun. Most asteroids are found between Jupiter and Mars:
the asteroid belt
▪ pulsar a type of star that is far away in space and produces ↑ radiation and RADIO WAVES
▪ quasar an object like a star that is far away in space and shines extremely brightly
▪ supernova a very large exploding star
▪ constellation a group of stars that forms a particular pattern and has a name:
The constellation of Orion is one of the most easily recognizable patterns of stars in the night sky.
▪ galaxy one of the large groups of stars that make up the universe:
Astronomers have detected a galaxy 11 billion light years away.
▪ the universe all space, including all the stars and planets:
How many planets in the universe have life?