Dictionary![]() ![]() ra•di•umPronunciation: (rā'dē-um), [key] —n. 1. Chem.a highly radioactive metallic element whose decay yields radon gas and alpha rays. Symbol: Ra; at. wt.: 226; at. no.: 88. 2. a lustrous rayon or silk fabric constructed in plain weave and used in women's apparel, lining, and drapery. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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