Fission/ˈfɪʃn/ Definition 1 of 3Pro Tip 1/3Technical Term Used mainly in scientific contexts relating to nuclear physics and energy. The scientists discussed the efficiency of fission in the new reactor. Pro Tip 2/3Energy Release Emphasizes the significant amount of energy produced during the process. Harnessing the energy from fission can power entire cities. Pro Tip 3/3Nuclear Vocabulary Often used alongside words like 'reactor', 'chain reaction', and 'atomic'. A fission chain reaction in the reactor core generates heat.