• synonyms


[rey-dee-uh m]
  1. Chemistry. a highly radioactive metallic element whose decay yields radon gas and alpha rays. Symbol: Ra; atomic weight: 226; atomic number: 88.
  2. a lustrous rayon or silk fabric constructed in plain weave and used in women's apparel, lining, and drapery.
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Origin of radium

1895–1900; < New Latin, equivalent to Latin rad(ius) ray (see radius) + -ium -ium
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for radium

Historical Examples

  • Rntgen-rays and radium have descended from the sphere of miracles.

    Mountain Meditations

    L. Lind-af-Hageby

  • But I'd advise you to keep for yourself that information on the Pool of Radium.

  • But why, if you could pick me off the Earth, do you not draw the radium ores in the same way?

  • That radium stuff is what makes the funny light in that mine, then?

  • They must be protected from the direct rays of the radium, which is refined.

British Dictionary definitions for radium


    1. a highly radioactive luminescent white element of the alkaline earth group of metals. It occurs in pitchblende, carnotite, and other uranium ores, and is used in radiotherapy and in luminous paints. Symbol: Ra; atomic no: 88; half-life of most stable isotope, 226 Ra: 1620 years; valency: 2; relative density: 5; melting pt: 700°C; boiling pt: 1140°C
    2. (as modifier)radium needle
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Word Origin

C20: from Latin radius ray
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 radium


radioactive metallic element, 1899, from French radium, named 1898 after identification by Marie Curie and her husband, formed in Modern Latin from Latin radius "ray" (see radius). So called for its power of emitting energy in the form of rays.

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Online Etymology Dictionary, © 2010 Douglas Harper

radium in Medicine


n. Symbol Ra
  1. A luminescent, highly radioactive metallic element found in minute amounts in uranium ores, used as a neutron source for some research purposes, and formerly used in cancer radiotherapy; its most stable isotope is Ra 226 with a half-life of 1,622 years. Atomic number 88.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

radium in Science


  1. A rare, bright-white, highly radioactive element of the alkaline-earth group. It occurs naturally in very small amounts in ores and minerals containing uranium, and it is naturally luminescent. Radium is used as a source of radon gas for the treatment of disease and as a neutron source for scientific research. Its most stable isotope is Ra 226 with a half-life of 1,622 years. Atomic number 88; melting point 700°C; boiling point 1,737°C; valence 2. See Periodic Table.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

radium in Culture


A naturally occurring radioactive chemical element. Its symbol is Ra.

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Radium was discovered by the chemists Marie and Pierre Curie.
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.