[ 'ʌɪsəmə ]
■ noun
1》 Chemistry each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties.
2》 Physics each of two or more atomic nuclei with the same atomic number and mass number but different energy states.
Derivatives
~ic adjective
~ism noun
~ize or ~ise verb
Origin
C19: from Gk ~ēs 'sharing equally', from isos 'equal' + meros 'a share'.