1
: a splitting or breaking up into parts
2
: reproduction by spontaneous division of the body into two or more parts each of which grows into a complete organism
3
: the splitting of an atomic nucleus resulting in the release of large amounts of energy
fissioned; fissioning; fissions
: to undergo fission
: to cause to undergo fission
Examples of fission in a Sentence
Recent Examples on the Web
New Atlas, 20 Oct. 2025
In such a cycle, used nuclear fuel is reprocessed to separate plutonium and other actinides from fission products.
—Aman Tripathi, Interesting Engineering, 18 Sep. 2025
Washington Post, 28 Apr. 2022
Anyone can see that fissioning uranium 235 or plutonium can be used to generate electricity.
—Scientific American, 1 Jan. 2018
See All Example Sentences for fission
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Noun
These are fed through a hopper into the reactor vessel to produce a self-regulating fission reaction and are cooled by helium gas that carries off the heat to a heat exchanger to generate steam for electrical generators.
—New Atlas, 20 Oct. 2025
In such a cycle, used nuclear fuel is reprocessed to separate plutonium and other actinides from fission products.
—Aman Tripathi, Interesting Engineering, 18 Sep. 2025
Verb
Most atoms do not fission, but the isotopes of certain elements, such as uranium-235, are fissile.
—Washington Post, 28 Apr. 2022
Anyone can see that fissioning uranium 235 or plutonium can be used to generate electricity.
—Scientific American, 1 Jan. 2018
See All Example Sentences for fission
Cite this Entry
“Fission.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/fission. Accessed 31 Oct. 2025.
Copy CitationKids Definition
fission
1 of 2 noun
fis·sion
ˈfish-ən 
also ˈfizh-
1
: a splitting or breaking up into parts
2
: a method of reproduction in which a living cell or body divides into two or more parts each of which grows into a whole new individual
3
: the splitting of an atomic nucleus resulting in the release of large amounts of energy
fission
2 of 2 verb
fissioned; fissioning
ˈfish-(ə-)niŋ,
ˈfizh-
: to go through or cause to go through fission
Medical Definition
fission
noun
fis·sion
ˈfish-ən also ˈfizh-
1
: a method of reproduction in which a living cell or body divides into two or more parts each of which grows into a whole new individual
2
a
b
: the splitting of an atomic nucleus resulting in the release of large amounts of energy
called also nuclear fission
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