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
"Homeowners in regions with granite bedrock often install special ventilation systems to reduce dangerous levels of radon gas that seep up from beneath their floors."
The chemical element (symbol Rn, formerly Ro) with atomic number 86. It is an odorless, colorless, chemically inert but radioactive noble gas.
"The air quality test revealed dangerously high levels of radon seeping from the soil beneath our basement floor."
The name radon is a contraction of "radium emanation," reflecting that the element was discovered as a product of radium's radioactive decay. It also incorporates the suffix "-on," which is used to denote noble gases.