/ray"dee euhm/ , 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.
[ 1895-1900; rad ( ius ) ray (see RADIUS) + -ium -IUM ]