Atomic fission, also known as nuclear fission, is a process where the nucleus of an atom is split into two smaller nuclei, releasing a significant amount of energy. There are various synonyms for this term, such as nuclear splitting, nuclear division, atom breaking, and atomic cleavage. Additionally, the word fissile is used to describe materials that can undergo atomic fission, while fissionable is used to describe materials that can potentially undergo this process. The opposite of atomic fission is atomic fusion, which is the process of combining two nuclei to form a heavier nucleus, releasing energy. Synonyms for atomic fusion include nuclear fusion, thermonuclear fusion, and atomic combination.