Etymology 1 
Coined in 1914 by British chemist Frederick Soddy from Ancient Greek ἴσος (ísos, “equal; same”) and τόπος (tópos, “place”), because the different isotopes of a chemical element always occupy the same position in the periodic table of elements. Compare the synonymous Icelandic word samsæta.
isotope (plural isotopes)
- (physics) Any of two or more forms of an element where the atoms have the same number of protons, but a different number of neutrons within their nuclei. As a consequence, atoms for the same isotope will have the same atomic number but a different mass number (atomic weight).
Derived terms 
See also 
Etymology 2 
Related terms 
isotope (masculine and feminine, plural isotopes)
- isotopic (relating to isotopes)
isotope m (plural isotopes)
- vocative singular of isotopus