1. Roman Mythology. The supreme god, patron of the Roman state and brother and husband of Juno. He came to be identified with the Greek Zeus. Also called Jove.
2. Astronomy. The fifth planet from the sun, the largest and most massive in the solar system, having a sidereal period of revolution about the sun of 11.86 years at a mean distance of 778 million kilometers (483 million miles), a mean diameter of approximately 142,000 kilometers (88,000 miles), and a mass approximately 318 times that of Earth.

[Latin Iūpiter.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.