one of two or more atoms with the same atomic number but with different numbers of neutrons
"Carbon-14 is an unstable isotope that differs from common carbon only by having extra neutrons in its nucleus."
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 of isotopes will have the same atomic number but a different mass number.
"Scientists use carbon-14, a specific isotope with extra neutrons in its nucleus, to determine the age of ancient fossils."
To define or demonstrate an isotopy of (one map with another).
"The mathematician proved that the two complex functions are isotopic by constructing a continuous deformation between them without tearing."