ˈ ̷ ̷ ̷ ̷ at iso- +_mə(r) noun
( -s )
Etymology: International Scientific Vocabulary, back-formation from isomeric; probably originally formed in German
1. : a compound, radical, or ion isomeric with one or more others
2. : a nuclide isomeric with one or more others
a metastable isomer
— called also nuclear isomer