WordNet (r) 3.0 (2006):

meitnerium
    n 1: a radioactive transuranic element [syn: meitnerium, Mt,
         element 109, atomic number 109]

The Elements (07Nov00):

meitnerium
Symbol: Mt
Atomic number: 109
Atomic weight: (266)
Half-life of approximately 5ms. The creation of this element
demonstrated
that fusion techniques could indeed be used to make new, heavy nuclei.
Made and identified by physicists of the Heavy Ion Research Laboratory,
Darmstadt, West Germany in 1982. Named in honor of Lise Meitner the
Austrian physicist.