cesium

Or cae·si·um

[see-zee-uhm]

noun

1. a rare, highly reactive, soft, metallic element of the alkali metal group, used chiefly in photoelectric cells. Cs; 132.905; 55; 1.9 at 20°C; melts at 28.5°C.

cesium

/ ˈsiːzɪəm /

noun

1. the usual US spelling of caesium

cesium

1. A soft, ductile, silvery-white element of the alkali group. It is liquid at room temperature and is the most reactive of all metals. Cesium is used to make photoelectric cells, electron tubes, and atomic clocks. Atomic number 55; atomic weight 132.905; melting point 28.5°C; boiling point 690°C; specific gravity 1.87; valence 1.

2. See Periodic Table

Word History and Origins

Origin of cesium¹

1930–35; < New Latin, special use of Latin caesium, neuter of caesius bluish-grey; -ium