ˈ ̷ ̷ ̷ ̷ˌtōp noun
( -s )
Etymology: is- + -tope (from Greek topos place) — more at topic
1.
a. : one of two or more species of atoms of the same chemical element that have the same atomic number and occupy the same position in the periodic table and that are nearly identical in chemical behavior but differ in atomic mass or mass number and so behave differently in the mass spectrograph, in radioactive transformations, and in physical properties (as diffusibility in the gaseous state) and may be detected and separated by means of these differences
deuterium and tritium are isotopes of hydrogen
especially : one such species of atom or a mixture of such species of atoms prepared for use as a tracer or in medicine — usually indicated for a specific element by the mass number following the name of the element or written superior to the symbol of the element (as carbon 14, C 14 , or 14 C); compare radioisotope
b. : the nucleus of such a species of atom
2. : nuclide