- radon, Rn, atomic number 86 - 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
--1 is a kind of chemical element, element; noble gas, inert gas, argonon
- registered nurse, RN - a graduate nurse who has passed examinations for registration
--2 is a kind of nurse
--2 has particulars: nurse-midwife; nurse practitioner, NP, nurse clinician