Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A rare, brilliant white, luminescent, highly radioactive metallic element found in very small amounts in uranium ores, having 13 isotopes with mass numbers between 213 and 230, of which radium 226 with a half-life of 1,622 years is the most common. It is used in cancer radiotherapy, as a neutron source for some research purposes, and as a constituent of luminescent paints. Atomic number 88; melting point 700°C; boiling point 1,737°C; valence 2. See Table at element.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. a radioactive metallic chemical element (symbol Ra) with an atomic number of 88.

from the GNU version of the Collaborative International Dictionary of English

  • n. An intensely radioactive metallic element found (combined) in minute quantities in pitchblende, and various other uranium minerals. Symbol, Ra; atomic weight, 226.4. Radium was discovered by M. and Mme. Curie, of Paris, who in 1902 separated compounds of it by a tedious process from pitchblende. Its compounds color flames carmine and give a characteristic spectrum. It is divalent, resembling barium chemically. The main isotope of radium found in pitchblende, radium-226, has a half-life of 1620 years, decaying first by alpha emission to radon.

from The Century Dictionary and Cyclopedia

  • n. A chemical element of very remarkable character, discovered in 1898 by Mme. Sklodowska Curie, working with her husband and M. Bémont.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. an intensely radioactive metallic element that occurs in minute amounts in uranium ores

Etymologies

Latin radius, ray + -ium.
(American Heritage® Dictionary of the English Language, Fourth Edition)
radio- (from radioactive) + -ium (Wiktionary)

Examples

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