[ roo-bid-ee-uh m ]
/ ruˈbɪd i əm /

noun Chemistry.

a silver-white, metallic, active element resembling potassium, used in photoelectric cells and radio vacuum tubes. Symbol: Rb; atomic weight: 85.47; atomic number: 37; specific gravity: 1.53 at 20°C.

Origin of rubidium

1860–65; < New Latin, equivalent to Latin rūbid(us) red (in allusion to the two red lines in its spectrum) + -ium -ium


ru·bid·ic, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for rubidium

British Dictionary definitions for rubidium

/ (ruːˈbɪdɪəm) /


a soft highly reactive radioactive element of the alkali metal group; the 16th most abundant element in the earth's crust (310 parts per million), occurring principally in pollucite, carnallite, and lepidolite. It is used in electronic valves, photocells, and special glass. Symbol: Rb; atomic no: 37; atomic wt: 85.4678; half-life of 87 Rb: 5 × 10 11 years; valency: 1, 2, 3, or 4; relative density: 1.532 (solid), 1.475 (liquid); melting pt: 39.48°C; boiling pt: 688°C

Derived forms of rubidium

rubidic, adjective

Word Origin for rubidium

C19: from New Latin, from Latin rubidus dark red, with reference to the two red lines in its spectrum
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medicine definitions for rubidium

[ rōō-bĭdē-əm ]

n. Symbol Rb

A soft metallic element of the alkali group. Atomic number 37.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for rubidium

[ rōō-bĭdē-əm ]


A soft, silvery-white metallic element of the alkali group. It ignites spontaneously in air and reacts violently with water. Rubidium is used in photoelectric cells, in making vacuum tubes, and in radiometric dating. Atomic number 37; atomic weight 85.47; melting point 38.89°C; boiling point 688°C; specific gravity (solid) 1.532; valence 1, 2, 3, 4. See Periodic Table.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.