organoarsenic

The story

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

From organo- + arsenic.