The story
- Latinradius
- Frenchradio-
- Proto-Indo-European*h₂eǵ-
- Proto-Indo-European*h₂éǵeti
- Proto-Italic*agō
- Latinagō
- Ancient Greekἐνεργητικός (energētikós)
- Latināctīvu
- Old Frenchactif
- Frenchactif
- Frenchradio(actif)
- Frenchradium
- Englishradium
- Proto-Indo-European*h₁éǵʰ
- Proto-Indo-European*h₁éǵʰs
- Proto-Italic*eks
- Latinex
- Latinē
- Proto-Indo-European*meh₂-
- Proto-Indo-European*meh₂no-
- Proto-Italic*māno-
- Latinmānō
- Latinmānāre
- Latinēmānāre
- Englishemanate
- Englishemanation
- Englishradium emanation
- English todayradon
Contraction of radium emanation, since the element appears in the radioactive decay of radium. By surface analysis, radio- + -on (“suffix for noble gases”).
Etymology from Wiktionary, CC BY-SA 4.0.