/uy som"euh riz'euhm/ , n.
1. Chem. 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 CH 3 OCH 3 and CH 3 CH 2 OH, or in the arrangement of their atoms in space and therefore in one or more properties. Cf. optical isomerism, stereoisomerism .
2. Also called nuclear isomerism . Physics. the relation of two or more nuclides that have the same atomic number and mass number but different energy levels and half-lives.
3. Chem. , Physics. the phenomenon characterized by such a relation.
4. the state or condition of being isomerous.
[ 1830-40; ISOMER(IC) + -ISM ]