cesium
/ˈsiziəm/
noun
- A soft, silvery-white metallic chemical element (symbol Cs) that is highly reactive and used in atomic clocks, drilling fluids, and photoelectric cells.
- Cesium is used in atomic clocks because of its precise frequency.
- The scientist handled cesium carefully because it reacts violently with water.
- Cesium compounds are sometimes used in medical treatments for cancer.