(astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise direction
"After years of debate over whether to include Pluto, astronomers finally updated our solar system list to reflect the eight recognized planet that orbit the Sun."
any celestial body (other than comets or satellites) that revolves around a star
"The astronomers confirmed that the newly discovered object qualifies as a planet because it directly orbits our sun without being captured by another moon."
Each of the seven major bodies which move relative to the fixed stars in the night sky—the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn.
"The ancient astronomers tracked each planet as it wandered against the backdrop of fixed stars in the night sky."
In plain English: A planet is a large rock or gas ball that orbits around a star and has cleared its own path of other space debris.
"We watched the planet Venus rise over the horizon at dawn."
Usage: In modern usage, a planet is any celestial body that orbits a star, not one of the historical seven wanderers including the Sun or Moon. Use this term today to refer specifically to objects like Earth, Mars, or Jupiter that revolve around our Sun.
The word "planet" comes from the Ancient Greek term for "wanderer," which originally referred to the wandering stars visible in the night sky. It entered English via Middle English and Old French, retaining its meaning as celestial bodies that appear to move across the heavens.