Rubidium
Rubidium , noun
[New Latin, from Latin rubidus red, from rubere to be red. So called from two dark red spectroscopic lines by means of which it was discovered in the lepidolite from Rozena, Moravia. See Rubicund.]
(Chemistry) 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.