1. Greek Mythology. A nymph, beloved of Zeus and hated by Hera. Hera changed her into a bear, and Zeus then placed her in the sky as the constellation Ursa Major.
2. One of the four brightest satellites of Jupiter and the eighth in distance from the planet. Originally sighted by Galileo, it is the largest planetary satellite.

[Latin, from Greek Kallistō, perhaps from kallistos, superlative of kalos, beautiful.]

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.