astatine

UK: /ˈæstəˌtiːn/ US: (as′tə tēn′ -tin)

WordReference Random House Unabridged Dictionary of American English © 2026

as•ta•tine  (as′tə tēn′ -tin), n. [Chem.]

1. Chemistry a rare element of the halogen family. Symbol: At;
   at. no.: 85.

• Greek ástat(os) not steadfast, unstable (see astatic) + -ine²
• 1945–50

Collins Concise English Dictionary © HarperCollins Publishers::

astatine / ˈæstəˌtiːn -tɪn/ noun

1. a radioactive element of the halogen series: a decay product of uranium and thorium that occurs naturally in minute amounts and is artificially produced by bombarding bismuth with alpha particles. Symbol: At; atomic no: 85; half-life of most stable isotope, ²¹⁰At: 8.1 hours; probable valency: 1,3,5, or 7; melting pt: 302°C; boiling pt: 337°C (est)

Etymology: 20th Century: from Greek astatos unstable (see astatic) + -ine²