radon

noun
  1. Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas. Radon is formed as an intermediate step in the normal radioactive decay chains through which thorium and uranium slowly decay into lead. It is considered a health hazard due to its radioactivity. noun
    Radon gas can accumulate in homes, especially in basements and lower levels.
    The presence of radon in the air is a significant risk factor for lung cancer.