keemilise elemendi teisend, mis erineb teistest aatomituumas olevate neutronite arvu poolest, one of two or more varieties of a chemical element whose atoms have a common number of protons and electrons (i.e. their atomic number is the same) but which vary in the number of neutrons in their nucleus (i.e. their atomic weight, signified by their mass number, is different), разные формы химического элемента, имеющие общие химические свойства, тот же атомный номер, но неодинаковый атомный вес, forme distincte d’un élément caractérisé par la masse nucléaire de ses atomes