diarsenic

The story

1. Proto-Indo-European*dwóh₁
2. Proto-Indo-European*dwi-
3. Proto-Hellenic*dwi-
4. Ancient Greekδῐ- (dĭ-)
5. Latindi-
6. Englishdi-
7. Proto-Indo-European*ǵʰelh₃-
8. Proto-Indo-European*ǵʰl̥h₃enyom
9. Proto-Indo-Iranian*ȷ́ʰr̥Hanyam
10. Proto-Iranian*jr̥Hanyam
11. Old Median*zaranyam
12. Old Median*kā
13. Old Median*zaraniyakā
14. Middle Persian*zarnīk
15. Classical Syriacܙܪܢܝܟܐ (zarnīḵā)
16. Arabicالزَرْنِيخ (az-zarnīḵ)
17. Medieval Greekἀρσενικόν (arsenikón)
18. Latinarsenicum
19. Middle Frencharsenic
20. Middle Englisharsenik
21. Englisharsenic
22. English todaydiarsenic

From di- + arsenic.