The chemical element (symbol Rb) with an atomic number of 37. It is a soft, highly reactive alkali metal. / (countable) A single atom of this element.

plural of rubidium

(chemistry) any oxide of rubidium, but especially the yellow solid Rb₂O; it is a strong base, reacting strongly with water to form the hydroxide and with acids to form normal salts

(attributive) Designating a method of geological dating based on the relative amounts in rock of rubidium-87 and its beta-decay product, strontium-87.

plural of rubidium oxide

(inorganic chemistry) A white crystalline powder that is highly soluble in water, with the formula RbNO₃.