Definition of rubidium noun from the Oxford Advanced American Dictionary

 

rubidium

 noun
noun
NAmE//rʊˈbɪdiəm//
 
[uncountable](symbol Rb)
 
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a chemical element. Rubidium is a rare, soft, silver-colored metal that reacts strongly with water and burns when it is brought into contact with air.
See the Oxford Advanced Learner's Dictionary entry: rubidium