WordNet (r) 3.0 (2006):

ununpentium
    n 1: a radioactive transuranic element [syn: ununpentium,
         Uup, element 115, atomic number 115]

The Elements (07Nov00):

ununpentium
Symbol: Uup
Atomic number: 115
Atmic weight: 288
Ununpentium is the temporary name of a synthetic superheavy element in
the periodic table that has the temporary symbol Uup and has the atomic
number 115.
It is placed as the heaviest member of group 15 (VA) although a
sufficiently stable isotope is not known at this time that would allow
chemical experiments to confirm its position. It was first observed in
2003 and only about 30 atoms of ununpentium have been synthesized to
date,
with just 4 direct decays of the parent element having been detected.
Two
isotopes are currently known, Uup-287 and Uup-288, with 288Uup having
the
longer half-life of ~100 ms.