Learn how to say Planetology correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word planet:
a celestial body moving in an elliptical orbit round a star.
(the planet) the earth:
no generation has the right to pollute the planet
chiefly Astrology & historical a celestial body distinguished from the fixed stars by having an apparent motion of its own (including the moon and sun), especially with reference to its supposed influence on people and events:
the planets are presently influencing you in a positive way
The planets of the solar system are either gas giants—Jupiter, Saturn, Uranus, and Neptune—or smaller rocky bodies—Mercury, 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
what planet are you on?
British informal used to indicate that someone is out of touch with reality.
Middle English: from Old French planete, from late Latin planeta, planetes, from Greek planētēs ‘wanderer, planet’, from planan ‘wander’