The Collaborative International Dictionary of English v.0.48:

Uranium \U*ra"ni*um\, n. [NL., from Uranus the planet. See
   Uranus.] (Chem.)
   An element of the chromium group, found in certain rare
   minerals, as pitchblende, uranite, etc., and reduced as a
   heavy, hard, nickel-white metal which is quite permanent. Its
   yellow oxide is used to impart to glass a delicate
   greenish-yellow tint which is accompanied by a strong
   fluorescence, and its black oxide is used as a pigment in
   porcelain painting. Symbol U. Atomic weight 239.
   [1913 Webster]

   Note: Uranium was discovered in the state of an oxide by
         Klaproth in 1789, and so named in honor of Herschel's
         discovery of the planet Uranus in 1781.
         [1913 Webster] Uran-ocher

WordNet (r) 3.0 (2006):

uranium
    n 1: a heavy toxic silvery-white radioactive metallic element;
         occurs in many isotopes; used for nuclear fuels and nuclear
         weapons [syn: uranium, U, atomic number 92]

The Elements (07Nov00):

uranium
Symbol: U
Atomic number: 92
Atomic weight: (231)
White radioactive metallic element belonging to the actinoids. Three
natural isotopes, U-238, U-235 and U-234. Uranium-235 is used as the
fuel
for nuclear reactors and weapons. Discovered by Martin H. Klaproth in
1789.