The radioactive element whose name is derived from the Greek word for "unstable" is Astatine. Its name comes from the Ancient Greek term astatos (ἄστατος), meaning "unstable," reflecting its highly radioactive nature and short-lived isotopes

. Astatine has the atomic number 85 and is the rarest naturally occurring halogen. All its isotopes are radioactive, with the most stable isotope, astatine-210, having a half-life of only 8.1 hours

. The element was first synthesized in 1940 and named to continue the tradition of halogen names ending in "-ine," while highlighting its instability