nuclear fusion
noun /ˌnjuːkliə ˈfjuːʒn/
  /ˌnuːkliər ˈfjuːʒn/
 (also fusion)
 [uncountable] (physics)- the act or process of combining the nuclei (= central parts) of atoms to form a heavier nucleus, with energy being releasedTopics Physics and chemistryc1