chlorovinyldichloroarsine

The story

1. Proto-Indo-European*ǵʰelh₃-
2. Proto-Indo-European*ǵʰl̥h₃rós
3. Proto-Hellenic*kʰlōrós
4. Ancient Greekχλωρός (khlōrós)
5. Englishchloro-
6. Proto-Indo-European*weh₁y-?
7. Proto-Indo-European*wéyh₁ō
8. Proto-Italic*wīnom
9. Latinvīnum
10. Proto-Indo-European*swel-der.?
11. Ancient Greekῡ̔́λη (hū́lē)
12. Englishvinyl
13. Englishchlorovinyl
14. Proto-Indo-European*dwóh₁
15. Proto-Indo-European*dwi-
16. Proto-Hellenic*dwi-
17. Ancient Greekδῐ- (dĭ-)
18. Latindi-
19. Englishdi-
20. Englishchloro-
21. Englishdichloro-
22. Proto-Indo-European*ǵʰelh₃-
23. Proto-Indo-European*ǵʰl̥h₃enyom
24. Proto-Indo-Iranian*ȷ́ʰr̥Hanyam
25. Proto-Iranian*jr̥Hanyam
26. Old Median*zaranyam
27. Old Median*kā
28. Old Median*zaraniyakā
29. Middle Persian*zarnīk
30. Classical Syriacܙܪܢܝܟܐ (zarnīḵā)
31. Arabicالزَرْنِيخ (az-zarnīḵ)
32. Medieval Greekἀρσενικόν (arsenikón)
33. Latinarsenicum
34. Middle Frencharsenic
35. Middle Englisharsenik
36. Englisharsenic
37. Englisharsine
38. English todaychlorovinyldichloroarsine

From chlorovinyl + dichloro- + arsine.