from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The act or process of splitting into parts.
  • n. A nuclear reaction in which an atomic nucleus, especially a heavy nucleus such as an isotope of uranium, splits into fragments, usually two fragments of comparable mass, releasing from 100 million to several hundred million electron volts of energy.
  • n. Biology An asexual reproductive process in which a unicellular organism divides into two or more independently maturing daughter cells.
  • transitive v. To cause (an atom) to undergo fission.
  • intransitive v. To undergo fission.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The process whereby one item splits to become two.
  • n. The process of splitting the nucleus of an atom into smaller particles; nuclear fission
  • n. The process by which a bacterium splits to form two daughter cells.
  • v. To cause to undergo fission.
  • v. To undergo fission.

from the GNU version of the Collaborative International Dictionary of English

  • n. A cleaving, splitting, or breaking up into parts.
  • n. A method of asexual reproduction among the lowest (unicellular) organisms by means of a process of self-division, consisting of gradual division or cleavage of the into two parts, each of which then becomes a separate and independent organisms; as when a cell in an animal or plant, or its germ, undergoes a spontaneous division, and the parts again subdivide. See Segmentation, and Cell division, under Division.
  • n. A process by which certain coral polyps, echinoderms, annelids, etc., spontaneously subdivide, each individual thus forming two or more new ones. See Strobilation.
  • n. The act or process of disintegration of an atomic nucleus into two or more smaller pieces; called also nuclear fission. The process may be spontaneous or induced by capture of neutrons or other smaller nuclei, and usually proceeds with evolution of energy.

from The Century Dictionary and Cyclopedia

  • n. The act of cleaving, splitting, or breaking up into parts.
  • n. In biology, the automatic division of a cell or an independent organism into new cells or organisms; especially, such division as a process of multiplication or reproduction. Also fissuration. See cut under Paramecium.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy
  • n. reproduction of some unicellular organisms by division of the cell into two more or less equal parts


from The American Heritage® Dictionary of the English Language, 4th Edition

Latin fissiō, fissiōn-, a cleaving, from fissus, split; see fissi-.

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Latin fissiōnem, accusative singular of fissiō ("the act of breaking up"), from findō ("split, divide").



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  • "He (American biologist William A. Arnold) could have gone to Berkeley to pick up radioisotope technique, but would have missed living in Copenhagen, learning from de Hevesy - would have missed contributing a coinage to the gamble that is history.... 'Later that day Frisch looked me up and said, 'You work in a microbiology lab. What do you call the process in which one bacterium divides into two?' And I answered, 'binary fission'. He wanted to know if you could call if 'fission' alone, and I said you could'"

    -- From "The Making of the Atomic Bomb" by Richard Rhodes, Frisch referring to Otto Frisch, who with Lise Meitner first postulated nuclear fission.

    November 9, 2007