Definition of: fission

(fish′ən) noun
1. The act of splitting or breaking apart.
2. Biol. Spontaneous division of a cell or organism into new cells or organisms, especially as a mode of reproduction; cell division.
3. Physics The disintegration of the nucleus of a radioactive atom initiated by bombardment with nucleons or gamma rays, leading to the formation of nuclei of more stable atoms and the release of energy.
4. In astrophysics, the breaking up of a large gaseous body into separate masses subject to mutual attraction: regarded as the possible origin of binary and double stars. [<L fissio, -onis <fissus, pp. of findere split]
—fis′sion·a·ble adjective