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• nuclear fusion
  nuclear fusion

  noun

  fusion.
• fusion, nuclear
  fusion, nuclear

  The combining of two small atomic nuclei to form a larger nucleus, sometimes with the release of energy. (Compare nuclear fission.)

nuclear fusion

American  

[noo-klee-er fyoo-zhuhn, nyoo-] / ˈnu kli ər ˈfyu ʒən, ˈnyu- /

noun

1. fusion.

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nuclear fusion British  

noun

1. Sometimes shortened to: fusion.  a reaction in which two nuclei combine to form a nucleus with the release of energy Compare nuclear fission See also thermonuclear reaction

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fusion, nuclear Cultural  

1. The combining of two small atomic nuclei to form a larger nucleus, sometimes with the release of energy. (Compare nuclear fission.)

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Pronunciation

See nuclear ( def. ).

Discover More

The use of fusion as a controllable energy source on Earth is still in its experimental stages.

The fusion of hydrogen into helium releases huge amounts of energy and is the main energy source of stars, including the sun.

Hydrogen bombs use the energy of fusion.

Etymology

Origin of nuclear fusion

First recorded in 1895–1900

Example Sentences

Actual power from nuclear fusion “has seemingly always been 10 to 20 years away,” Levin said.

From MarketWatch • May 18, 2026

That’s roughly how much OpenAI founder Sam Altman proposed the company invest in Helion, a startup trying to generate energy through nuclear fusion.

From The Wall Street Journal • Apr. 23, 2026

Shares are down 63% over the past 12 months with investors seemingly unimpressed by its merger with nuclear fusion start-up TAE Technologies, announced in December.

From Barron's • Apr. 22, 2026

Being accused of attempting the impossible is not unusual for the scientists and engineers working on nuclear fusion projects around the world.

From BBC • Apr. 20, 2026

It assumes the existence of a nuclear fusion reactor— something much safer as well as more efficient than existing fission power plants.

From "Cosmos" by Carl Sagan