[yoo-rey-nee-uh m]

noun Chemistry.

a white, lustrous, radioactive, metallic element, occurring in pitchblende, and having compounds that are used in photography and in coloring glass. The 235 isotope is used in atomic and hydrogen bombs and as a fuel in nuclear reactors. Symbol: U; atomic weight: 238.03; atomic number: 92; specific gravity: 19.07.

Origin of uranium

From New Latin, dating back to 1790–1800; see origin at Uranus, -ium
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for uranium

Contemporary Examples of uranium

Historical Examples of uranium

  • To begin with metals, uranium melts at 1150 centigrade, and tungsten at 3370 and iridium at 2350.

    Pariah Planet

    Murray Leinster

  • It's not controllable enough and uranium isn't something we could carry by the ton.

    Islands of Space

    John W Campbell

  • Transpose it into platinum or uranium—anything good and heavy.

    The Galaxy Primes

    Edward Elmer Smith

  • Nova-Maurania was nearly 40 percent uranium, and who could resist that?

    Dead World

    Jack Douglas

  • In some varieties the oxide of uranium is also present in traces.

British Dictionary definitions for uranium



a radioactive silvery-white metallic element of the actinide series. It occurs in several minerals including pitchblende, carnotite, and autunite and is used chiefly as a source of nuclear energy by fission of the radioisotope uranium-235 . Symbol: U; atomic no: 92; atomic wt: 238.0289; half-life of most stable isotope, 238 U: 451 × 10 9 years; valency: 2-6; relative density: 18.95 (approx.); melting pt: 1135°C; boiling pt: 4134°C

Word Origin for uranium

C18: from New Latin, from Uranus ²; from the fact that the element was discovered soon after the planet
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for uranium

rare metallic element, 1797, named 1789 in Modern Latin by its discoverer, German chemist and mineralogist Martin Heinrich Klaproth (1743-1817), for the recently found planet Uranus (q.v.).

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for uranium



n. Symbol U

An easily oxidized radioactive toxic metallic element having 16 known isotopes, of which U 238 is the most naturally abundant. Atomic number 92.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for uranium




A heavy, silvery-white, highly toxic, radioactive metallic element of the actinide series. It has 14 known isotopes, of which U 238 is the most naturally abundant, occurring in several minerals. Fissionable isotopes, especially U 235, are used in nuclear reactors 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 Periodic Table.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Culture definitions for uranium


A chemical element that is naturally radioactive. An isotope of uranium, uranium 235, is the main fuel for nuclear reactors and atomic bombs (see also atomic bomb). Its symbol is U. (See fission and chain reaction.)

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.