- the relation of two or more compounds, radicals, or ions that are composed of the same kinds and numbers of atoms but differ from each other in structural arrangement (structural isomerism ), as CH3OCH3 and CH3CH2OH, or in the arrangement of their atoms in space and therefore in one or more properties.
- the relation of two or more nuclides that have the same atomic number and mass number but different energy levels and half-lives.
- the phenomenon characterized by such a relation.
- the state or condition of being isomerous.
- the existence of two or more compounds having the same molecular formula but a different arrangement of atoms within the molecule
- the existence of two or more nuclides having the same atomic numbers and mass numbers but different energy states
