[rey-dee-uh m]


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.

Nearby words

  1. radiovision,
  2. radisectomy,
  3. radish,
  4. radisson,
  5. radisson, pierre esprit,
  6. radium a,
  7. radium b,
  8. radium emanation,
  9. radium f,
  10. radium sulfate

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. 2019

Examples from the Web for radium

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

Word Origin for radium

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.

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for radium



n. 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.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for radium




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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Culture definitions for radium


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


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.