[f. CORONA 2, on the analogy of chemical names in -IUM.] An otherwise unknown element supposed to exist in a gaseous state in the sun’s corona. (Cf. HELIUM.)
1890. C. A. Young, Elem. Astron., vi. § 207. The characteristic feature of the visual spectrum [of the sun’s corona] is a bright line in the green … because it coincides with a dark line … on Kirchhoff’s map of the solar spectrum…. This dark line … is really a close double, one of its two components being due to iron, while the other is due to some unknown gaseous element, which has been called ‘Coronium’ after the analogy of Helium.
