beryllium

 
Pronunciation: /bəˈrɪlɪəm/

noun

[mass noun]
  • the chemical element of atomic number 4, a hard grey metal. (Symbol: Be)
  • Beryllium is the lightest of the alkaline earth metals, and its chief source is the mineral beryl. It is used in the manufacture of light corrosion-resistant alloys and in windows in X-ray equipment