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English definition of “radon”

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noun [U] uk   /ˈreɪ.dɒn/ us    /-dɑːn/ ( symbol Rn)
a chemical element that is a radioactive gas formed when radium decays and found naturally in rock and soil: Tests showed high radon levels.
(Definition of radon from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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