# rubidium

> English word · Noun · IPA /ˌɹuːˈbɪd.i.əm/ · frequency rank #77,166

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

## Etymology
A New Latin word derived by German chemist R. W. Bunsen in 1861, from Latin rūbidus (“red”) because its spectrum has two red lines.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/rubidium