Condition that occurs when two or more normal transitions have the same energy as a matter of coincidence, as opposed to because of symmetry conditions.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 651 (https://doi.org/10.1515/pac-2019-0203)