fission

Concise Oxford English Dictionary © 2008 Oxford University Press:
fission /ˈfɪʃ(ə)n/

▶noun

• 1 division or splitting into parts.

• 2 a reaction in which a heavy atomic nucleus splits in two, releasing much energy.

• 3 Biology reproduction by means of a cell or organism dividing into two or more new cells or organisms.

▶verb (chiefly of atoms) undergo fission.

– derivatives
fissionable adjective.

– origin C17: from L. fissio(n-), from findere ‘to split’.