fission fission /ˈfɪʃən/

noun

1. A nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy  ( fission , nuclear fission )
   a nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy
   
   
2. Reproduction of some unicellular organisms by division of the cell into two more or less equal parts  ( fission )
   reproduction of some unicellular organisms by division of the cell into two more or less equal parts