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[rey-dee-uh m] /ˈreɪ di əm/
Chemistry. a highly radioactive metallic element whose decay yields radon gas and alpha rays. Symbol: Ra; atomic weight: 226; atomic number: 88.
a lustrous rayon or silk fabric constructed in plain weave and used in women's apparel, lining, and drapery.
Origin of radium
1895-1900; < New Latin, equivalent to Latin rad(ius) ray (see radius) + -ium -ium Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for radium
  • If you have old-fashioned luminous dials on your clocks they were made using radium, the glow was radiation.
  • Discovered that uranium emits radiation naturally, and isolated two new radioactive elements-polonium and radium.
  • Or all the radium poisonings back when radiation was fashionable.
  • In her work, she established the nature of radiation and beta rays, and discovered and isolated polonium and radium.
  • UP to the time of the discovery of radium anthracite coal represented about the highest known degree of stored energy.
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, 226Ra: 1620 years; valency: 2; relative density: 5; melting pt: 700°C; boiling pt: 1140°C
  2. (as modifier): radium needle
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
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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.

Online Etymology Dictionary, © 2010 Douglas Harper
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radium in Medicine

radium ra·di·um (rā'dē-əm)
Symbol Ra
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; melting point 700°C; boiling point 1,140°C; valence 2.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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radium in Science
Symbol Ra
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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radium in Culture

radium definition

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

Note: Radium was discovered by the chemists Marie and Pierre Curie.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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