A fissionable material that is especially amenable to fission and therefore readily usable for the core of a nuclear weapon. Uranium-235 and plutonium-239 are examples of fissile materials.
A material consisting of atoms whose nuclei can be split when irradiated with low energy (ideally, zero energy) neutrons. Well-known examples are plutonium-239 and uranium-235.
Material that can be caused to undergo atomic fission when bombarded by neutrons. The most important fissionable materials are uranium-235, plutonium-239, and uranium-233.