noun
: a light isotope of uranium of mass number 235 that is physically separable from natural uranium or is formed from plutonium by emission of a helium nucleus, that as the parent of the actinium series undergoes very slow radioactive disintegration, and that when bombarded with slow neutrons undergoes rapid fission into smaller atoms (as strontium and xenon or barium and krypton) together with much radiation and atomic energy, and that is used in power plants and atom bombs — symbol U 235 or 235 U; called also actinouranium