Io

early 15c., from Latin titan, from Greek titan, "a member of a mythological race of giants" (originally six sons and six daughters of Gaia and Uranus) who were overthrown by Zeus and the other gods. The war was a popular theme for Greek artists and writers. The name is perhaps from titō "sun, day," which probably is a loan-word from a language of Asia Minor. The sense of "person or thing of enormous size or ability" is by 1828.

Titan was given as a name to planet Saturn's largest satellite in 1831 (Greek Kronos, equivalent of Roman Saturn, was leader of the titans). It was discovered 1655 by Dutch astronomer Christiaan Huygens, who named it Saturni Luna "moon of Saturn," but others soon were found and thereafter they generally were known by number only. But as new ones were being found orbiting between the known moons, the numbering kept changing. William Herschel proposed giving the multiplying moons of Saturn and Jupiter suitable proper names out of mythology, a proposal readily accepted by the other astronomers. Related: Titaness; titanian.