Pronunciation: ( jOO'pi-tur),[key] —n. 1. Also called Jove. the supreme deity of the ancient Romans: the god of the heavens and of weather. Cf. Zeus. 2. Astron.the planet fifth in order from the sun, having an equatorial diameter of 88,729 mi. (142,796 km), a mean distance from the sun of 483.6 million mi. (778.3 million km), a period of revolution of 11.86 years, and at least 14 moons. It is the largest planet in the solar system. See table under planet. 3. Mil.a medium-range U.S. ballistic missile of the 1950s, powered by a single liquid-fueled rocket engine.