nonarsenical

The story

1. Proto-Indo-European*né
2. Proto-Germanic*ne
3. Proto-Indo-European*ís?
4. Proto-Indo-European*h₁óynos
5. Proto-Germanic*ainaz
6. Proto-Germanic*nainaz
7. Proto-West Germanic*nain
8. Old Englishnān
9. Middle Englishnon
10. Old Englishnān
11. Old Englishnān-
12. Middle Englishnon-
13. Englishnon-
14. Proto-Indo-European*ǵʰelh₃-
15. Proto-Indo-European*ǵʰl̥h₃enyom
16. Proto-Indo-Iranian*ȷ́ʰr̥Hanyam
17. Proto-Iranian*jr̥Hanyam
18. Old Median*zaranyam
19. Old Median*kā
20. Old Median*zaraniyakā
21. Middle Persian*zarnīk
22. Classical Syriacܙܪܢܝܟܐ (zarnīḵā)
23. Arabicالزَرْنِيخ (az-zarnīḵ)
24. Medieval Greekἀρσενικόν (arsenikón)
25. Latinarsenicum
26. Proto-Indo-European*h₂el-
27. Proto-Indo-European*h₂élisder.?
28. Englisharsenical
29. English todaynonarsenical

From non- + arsenical.