WordNet (r) 3.0 (2006):

astatine
    n 1: a highly unstable radioactive element (the heaviest of the
         halogen series); a decay product of uranium and thorium
         [syn: astatine, At, atomic number 85]

The Elements (07Nov00):

astatine
Symbol: At
Atomic number: 85
Atomic weight: (210)
Radioactive halogen element. Occurs naturally from uranium and thorium
decay. At least 20 known isotopes. At-210, the most stable, has a
half-life of 8.3 hours. Synthesized by nuclear bombardment in 1940 by
D.R.
Corson, K.R. MacKenzie and E. Segre at the University of California.