radon

n. (Chemistry) radioactive gaseous chemical element (produced by the breakdown of radium)

Radon (IPA: ) is a chemical element  that has the symbol Rn and atomic number 86. Radon is a radioactive noble gas that is formed by the decay of radium. It is one of the heaviest gases and is considered to be a health hazard. The most stable isotope is 222Rn which has a half-life of 3.8 days and is used in radiotherapy. Radon is a significant contaminant that affects indoor air quality worldwide. Radon gas from natural sources can accumulate in buildings and reportedly causes 21,000 lung cancer deaths per year in the United States alone.
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Noun
1. a radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health
(synonym) Rn, atomic number 86
(hypernym) chemical element, element

n. (Chemistry) radon, radioactive gaseous chemical element (produced by the breakdown of radium)

n. radon, (Chemistry) radioactive gaseous chemical element (produced by the breakdown of radium)