n. & v.
n. 1 Physics the spontaneous or impact-induced splitting of a heavy atomic nucleus, accompanied by a release of energy. 2 Biol. the division of a cell etc. into new cells etc. as a mode of reproduction.
v.intr. & tr. undergo or cause to undergo fission. fission bomb an atomic bomb. fissionable adj.
[ L fissio (as FISSURE) ]