The story
- Proto-Indo-European*déḱm̥
- Proto-Hellenic*dékə
- Ancient Greekδέκᾰ (dékă)
- Ancient Greekδεκάς (dekás)
- Late Latindecas
- Frenchdéca-
- Englishdeca-
- Frenchméthylène
- Englishmeth(ylene)
- New Latinammōnium
- Englishammonium
- Englishonium
- English todaydecamethonium
From deca- + meth(ylene) + -onium (“quaternary ammonium compound”).
Etymology from Wiktionary, CC BY-SA 4.0.