noun Chemistry.

  1. a chemically inert, gaseous, short-lived isotope of radon that is a member of the actinium series. Symbol: An; atomic number: 86; atomic weight: 219.


  1. a radioisotope of radon that is a decay product of radium. Symbol: An or 219 Rn; atomic no: 86; half-life: 3.92s
  2. another name for actinide

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