hexadecarsenide

The story

1. Proto-Indo-European*swéḱs
2. Proto-Hellenic*hwéks
3. Ancient Greekἕξ (héx)
4. Ancient Greekἑξα- (hexa-)
5. Latinhexa-
6. Englishhexa-
7. Proto-Indo-European*déḱm̥
8. Proto-Hellenic*dékə
9. Ancient Greekδέκᾰ (dékă)
10. Ancient Greekδεκάς (dekás)
11. Late Latindecas
12. Frenchdéca-
13. Englishdeca-
14. Englishhexadeca-
15. Proto-Indo-European*ǵʰelh₃-
16. Proto-Indo-European*ǵʰl̥h₃enyom
17. Proto-Indo-Iranian*ȷ́ʰr̥Hanyam
18. Proto-Iranian*jr̥Hanyam
19. Old Median*zaranyam
20. Old Median*kā
21. Old Median*zaraniyakā
22. Middle Persian*zarnīk
23. Classical Syriacܙܪܢܝܟܐ (zarnīḵā)
24. Arabicالزَرْنِيخ (az-zarnīḵ)
25. Medieval Greekἀρσενικόν (arsenikón)
26. Latinarsenicum
27. Middle Frencharsenic
28. Middle Englisharsenik
29. Englisharsenic
30. Proto-Indo-European*dʰeh₁-
31. Englisharsenide
32. English todayhexadecarsenide

From hexadeca- + arsenide.