[ fish-uhn ]
See synonyms for fission on
  1. the act of cleaving or splitting into parts.

  2. Also called nuclear fission .Physics. the splitting of the nucleus of an atom into nuclei of lighter atoms, accompanied by the release of energy.: Compare fusion (def. 4).

  1. Biology. the division of an organism into new organisms as a process of reproduction.

verb (used without object)
  1. Physics. to undergo fission.

verb (used with object)
  1. Physics. to cause to undergo fission.

Origin of fission

First recorded in 1835–45; from Latin fissiōn- (stem of fissiō ) “a splitting, dividing,” equivalent to fiss(us) “divided” + -iōn- noun-forming suffix; see fissi-, -ion;def. 2 was first recorded in 1935–40

Words that may be confused with fission

Words Nearby fission Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use fission in a sentence

British Dictionary definitions for fission


/ (ˈfɪʃən) /

  1. the act or process of splitting or breaking into parts

  2. biology a form of asexual reproduction in single-celled animals and plants involving a division into two or more equal parts that develop into new cells

  1. short for nuclear fission

Origin of fission

C19: from Latin fissiō a cleaving

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for fission


[ fĭshən ]

  1. The splitting of an unstable atomic nucleus into two or more nuclei. Fission occurs spontaneously, generally when a nucleus has an excess of neutrons, resulting in the inability of the strong force to bind the protons and neutrons together. The fission reaction used in many nuclear reactors and bombs involves the absorption of neutrons by uranium-235 nuclei, which immediately undergo fission, releasing energy and fast neutrons. Compare fusion.

  2. A process of asexual reproduction in which a single cell splits to form two identical, independent cells. In fission, the chromosomal DNA replicates before the cell divides. Most bacteria and other prokaryotes reproduce by means of fission. Also called binary fission

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.