Literally meaning: equal or same position
Origin: Anc Greek
ίσος/isos(=equal) combining form ισο-/iso- eg isomer, isopod
τόπος/topos(=place) because despite the different atomic weights, the various forms of an element occupy the same place on the periodic table.
by British chemist Frederick Soddy (1877-1956) on suggestion of Margaret Todd who had said of isotopes, "Put colloquially, their atoms have identical outsides but different insides." In a short letter to the editor of Nature, published on December 4, 1913, he proposed the term isotope to designate chemically identical elements with different atomic weights
Isotopes are the different possible versions of a particular element which have differing numbers of neutrons (a subatomic particle contained in the have the same atomic numbers but different mass numbers.