Here I mean the kind of Greek that Newton was familiar with: classical Greek. Anyway, in the periodic table of the elements, the number of protons (i.e. the electric charge) of each element is given along with an atomic weight, usually not a whole number. The reason for the fractional atomic weights is the presence of isotopes, in places the atomic weight is a whole number because there the most stable isotope is listed. So anyway, it seems that these isotopes are so called because they are in the same place in the table, hence one could assume that's what isotope means in Greek: "same place". But I think topos can also mean standing or status. And what about tropos, seen in isotropic? What did the Roman language do with these?