Real Dictionary

plutonium
uncountable noun: Plutonium is a radioactive element used especially in nuclear weapons and as a fuel in nuclear power stations.

plutonium in American English
a radioactive, metallic chemical element, one of the actinides, found in trace quantities in native uranium ores and produced by bombarding uranium with deuterons: symbol, Pu; at. no., 94: its most important isotope (plutonium-239) is used in nuclear weap
noun: 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; at. no.: 94

plutonium in British English
noun: a highly toxic metallic transuranic element. It occurs in trace amounts in uranium ores and is produced in a nuclear reactor by neutron bombardment of uranium-238. The most stable and important isotope, plutonium-239, readily undergoes fission and is used