WordNet (r) 3.0 (2006):

atomic number 94
    n 1: a solid silvery grey radioactive transuranic element whose
         atoms can be split when bombarded with neutrons; found in
         minute quantities in uranium ores but is usually
         synthesized in nuclear reactors; 13 isotopes are known with
         the most important being plutonium 239 [syn: plutonium,
         Pu, atomic number 94]