Source : WordNet®

Rn
     n 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 [syn: {radon}, {atomic
          number 86}]
     2: a graduate nurse who has passed examinations for
        registration [syn: {registered nurse}]