a hypothetical element once thought to be present in emission nebulae because of certain unidentified spectral lines, now known to be forbidden transitions of oxygen and nitrogen ions.
Origin of nebulium
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for nebulium
Historical Examples of nebulium
The whole thing aglow with the green light of nebulium and blazing with the stars behind it.Out Around Rigel
Robert H. Wilson