Rubidium /(?)/

Ru·bid·i·um

Rubidium

n.
  1. A rare metallic element of the alkali metal series, atomic number 37. It occurs quite widely, but in small quantities, and always combined. It is isolated as a soft yellowish white metal, analogous to potassium in most of its properties. Symbol Rb. Atomic weight, 85.48. (Chem.)