/plooh toh"nee euhm/ , n. Chem., Physics.
a transuranic element with a fissile isotope of mass number 239 (plutonium 239) that can be produced from non-fissile uranium 238, as in a breeder reactor. Symbol: Pu; at. no.: 94.
[ 1940-45; Ploúton PLUTO + -IUM ]