perchloropentacyclodecane

The story

1. Proto-Indo-European*per-der.?
2. Proto-Indo-European*pér
3. Proto-Italic*per
4. Latinper
5. Proto-Indo-European*per-
6. Proto-Italic*peri-
7. Latinper-
8. Englishper-
9. Proto-Indo-European*ǵʰelh₃-
10. Proto-Indo-European*ǵʰl̥h₃rós
11. Proto-Hellenic*kʰlōrós
12. Ancient Greekχλωρός (khlōrós)
13. Englishchloro-
14. Proto-Indo-European*pénkʷe
15. Proto-Hellenic*pénkʷe
16. Ancient Greekπέντε (pénte)
17. Ancient Greekπεντᾰ- (pentă-)
18. Englishpenta-
19. Proto-Indo-European*kʷelh₁-redup.
20. Proto-Indo-European*kʷékʷlos
21. Proto-Hellenic*kʷókʷlos
22. Proto-Hellenic*kúklos
23. Ancient Greekκύκλος (kúklos)
24. Late Latincyclus
25. Middle Englishcicle
26. Englishcycle
27. Ancient Greekκύκλος (kúklos)
28. Ancient Greekκυκλῐκός (kuklĭkós)
29. Classical Latincyclicu
30. Middle Frenchcyclique
31. Frenchcyclique
32. Classical Latincyclicus
33. Englishcyclic
34. Englishcyclo-
35. Proto-Indo-European*déḱm̥
36. Proto-Hellenic*dékə
37. Ancient Greekδέκᾰ (dékă)
38. Ancient Greekδεκάς (dekás)
39. Late Latindecas
40. Frenchdéca-
41. Englishdeca-clip.
42. Englishdec-
43. Englishdecane
44. English todayperchloropentacyclodecane

From per- + chloro- + penta- + cyclo- + decane.