u·ra·ni·um   Pronunciation Key  (y-rn-m)
n. Symbol U

A heavy silvery-white metallic element, radioactive and toxic, easily oxidized, and having 14 known isotopes of which U 238 is the most abundant in nature. The element occurs in several minerals, including uraninite and carnotite, from which it is extracted and processed for use in research, nuclear fuels, and nuclear weapons. Atomic number 92; atomic weight 238.03; melting point 1,132°C; boiling point 3,818°C; specific gravity 18.95; valence 2, 3, 4, 5, 6. See table at element.

[New Latin ranium, after ranus, Uranus. See Uranus.]

Word History: Some chemical elements, such as ytterbium and berkelium, derive their names from the places they were discovered, but the element uranium owes its name to an earlier scientific discovery, that of the planet Uranus. Sir William Herschel, who discovered Uranus in 1781, wanted to name the planet Georgium sidus, “the Georgian planet,” in honor of George III; others called it Herschel. Eventually convention prevailed and the planet came to be called Uranus, like Mercury and Pluto the name of a heavenly deity in classical mythology. This god, called Ouranos in Greek (Latinized as Uranus), was chosen because he was the father of Saturn (Greek Kronos), the deity of the planet next in line, who himself was the father of Jupiter (Greek Zeus), the deity of the next planet. The name of this new planet Uranus was then used in the name of a new chemical element discovered eight years later by M.H. Klaproth. Klaproth, a German scientist, gave it the Latin name uranium in honor of the discovery of Uranus. Uranium passed into English shortly thereafter, being first recorded in the third edition of the Encyclopedia Britannica, published in 1797.