A nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy WordNet 3.0 & Open English WordNet

Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. Wikipedia

A nuclear reaction splitting an atom into multiple parts Wikidata

The division of an atomic nucleus into parts of comparable mass; usually restricted to heavier nuclei such as isotopes of uranium, plutonium, and thorium. OmegaWiki

The splitting of a heavy nucleus into two roughly equal parts (which are nuclei of lower-mass elements), accompanied by the release of a relatively large amount of energy in the form of kinetic energy of the two parts and in the form of emission of neutrons and gamma rays (source: LBL). OmegaWiki

Short for nuclear fission: The process of splitting the nucleus of an atom into smaller particles. Wiktionary

A nuclear reaction in which a large nucleus splits into smaller ones with the simultaneous release of energy. Wiktionary

Atom-splitting nuclear reaction. Wiktionary (translation)