Meaning of cesium

ce•si•um

Pronunciation: (sē'zē-um), [key]
— n.
  1. a rare, highly reactive, soft, metallic element of the alkali metal group, used chiefly in photoelectric cells. Symbol: Cs; at. wt.: 132.905; at. no.: 55; sp. gr.: 1.9 at 20°C; melts at 28.5°C.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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