WordNet (r) 3.0 (2006):

ununtrium
    n 1: a radioactive transuranic element [syn: ununtrium, Uut,
         element 113, atomic number 113]

The Elements (07Nov00):

ununtrium
Symbol: Uut
Atomic number: 113
Atmic weight: 284
Ununtrium is the temporary name of a synthetic element with the
temporary
symbol Uut and atomic number 113. It is placed as the heaviest member of
the group 13 (IIIA) elements although a sufficiently stable isotope is
not
known at this time that would allow chemical experiments to confirm its
position. It was first detected in 2003 in the decay of element 115 and
was synthesized directly in 2004. Only eight atoms of ununtrium have
been
observed to date. The longest-lived isotope known is 284113 with a
half-life of ~500 ms.