diphosphomevalonate

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*bʰeh₂-
8. Proto-Indo-European*bʰéh₂os
9. Proto-Hellenic*pʰáwos
10. Ancient Greekφᾰ́ος (phắos)
11. Ancient Greekφῶς (phôs)
12. Proto-Indo-European*bʰer-
13. Proto-Indo-European*bʰéreti
14. Proto-Hellenic*pʰérō
15. Ancient Greekφέρω (phérō)
16. Ancient Greekφωσφόρος (phōsphóros)
17. Latinphōsphorus
18. Englishphosphorus
19. Englishphospho-
20. Proto-Indo-European*médʰu
21. Proto-Hellenic*métʰu
22. Ancient Greekμέθυ (méthu)
23. Proto-Indo-European*swel-der.?
24. Ancient Greekῡ̔́λη (hū́lē)
25. GermanMethy
26. Englishmethyl
27. Englishvalerian
28. Englishvaleric
29. GermanKeton
30. Englishketone
31. Englishmevalonic
32. Englishmevalonate
33. English todaydiphosphomevalonate

From di- + phospho- + mevalonate.