Pronunciation: (plan'it),[key] —n. 1. Astron. a. Also called major planet. any of the nine large heavenly bodies revolving about the sun and shining by reflected light: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto in the order of their proximity to the sun.
b. a similar body revolving about a star other than the sun.
c. (formerly) a celestial body moving in the sky, as distinguished from a fixed star, applied also to the sun and moon.
2. Astrol.the sun, moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto: considered sources of energy or consciousness in the interpretation of horoscopes.