orthohydrogen

The story

1. Proto-Indo-European*h₃er-
2. Proto-Indo-European*dʰeh₁-
3. Proto-Indo-European*h₃érdʰeti?
4. Proto-Indo-European*h₃erdʰ-
5. Proto-Hellenic*ortʰwós
6. Ancient Greekὀρθός (orthós)
7. Englishortho-
8. Proto-Indo-European*wed-
9. Proto-Indo-European*wódr̥
10. Proto-Hellenic*údōr
11. Ancient Greekῡ̆̔́δωρ (hū̆́dōr)
12. Ancient Greekὑδρο- (hudro-)
13. Frenchhydro-
14. Proto-Indo-European*ǵenh₁-
15. Proto-Indo-European*ǵénh₁os
16. Proto-Hellenic*génos
17. Ancient Greekγένος (génos)
18. Frenchhydrogène
19. Englishhydrogen
20. English todayorthohydrogen

From ortho- + hydrogen.