(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 WordNet 3.0 & Open English WordNet

A planet is a large, rounded astronomical body that is neither a star nor its remnant. Wikipedia

Celestial body directly orbiting a star or stellar remnant Wikidata

A large, heavy body, which does not produce energy by nuclear fusion, moving in a stable elliptical orbit around a star. OmegaWiki

Any of the 8 celestial bodies which orbit the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (a celestial body that fits the 2006 IAU definition of planet). Wiktionary

A body which orbits the Sun directly and is massive enough to be in hydrostatic equilibrium (effectively meaning a spheroid) and to dominate its orbit; specifically, the eight major bodies of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. (Pluto was considered a planet until 2006 and has now been reclassified as a dwarf planet.). Wiktionary