▸nounthe chemical element of atomic number 86, a rare radioactive gas belonging to the noble gas series.(Symbol: Rn)
Radon is a product of the radioactive decay of radium and is used as a source of alpha particles in radiotherapy. Small quantities of the gas are also emitted naturally from the ground in granite-rich areas.
– ORIGIN early 20th century : from radium, on the pattern of argon.
EnglishOxford New American Dictionary
