Wikipedia logo The Simple English Wikipedia has an article on: Nuclear fusion Pronunciation enPR: fyōō’-zhən, IPA (key): /ˈfjuː.ʒən/ Audio (UK)(file) SAMPA: /"fju:.Z@n/ Noun Singular fusion Plural fusions (uncountable) Fusion is when two or more things come together as one. Synonyms: blend and merger (uncountable), (physics) In physics, nuclear fusion is when the nuclei of two or more atoms come together to make one new, heavier nucleus. Fusion reactions make a lot of energy. Related words fuse fusionalWikiwand - on Seamless Wikipedia browsing. On steroids.