arsenobetaine

The story

1. Proto-Indo-European*ǵʰelh₃-
2. Proto-Indo-European*ǵʰl̥h₃enyom
3. Proto-Indo-Iranian*ȷ́ʰr̥Hanyam
4. Proto-Iranian*jr̥Hanyam
5. Old Median*zaranyam
6. Old Median*kā
7. Old Median*zaraniyakā
8. Middle Persian*zarnīk
9. Classical Syriacܙܪܢܝܟܐ (zarnīḵā)
10. Arabicالزَرْنِيخ (az-zarnīḵ)
11. Medieval Greekἀρσενικόν (arsenikón)
12. Latinarsenicum
13. Middle Frencharsenic
14. Middle Englisharsenik
15. Englisharsenic
16. Englisharseno-
17. Latinbēta
18. Englishbetaine
19. English todayarsenobetaine

From arseno- + betaine.