hydrogenotrophic

The story

1. Proto-Indo-European*wed-
2. Proto-Indo-European*wódr̥
3. Proto-Hellenic*údōr
4. Ancient Greekῡ̆̔́δωρ (hū̆́dōr)
5. Ancient Greekὑδρο- (hudro-)
6. Frenchhydro-
7. Proto-Indo-European*ǵenh₁-
8. Proto-Indo-European*ǵénh₁os
9. Proto-Hellenic*génos
10. Ancient Greekγένος (génos)
11. Frenchhydrogène
12. Englishhydrogen
13. Proto-Hellenic*tʰrépʰō
14. Ancient Greekτρέφω (tréphō)
15. Ancient Greekτροφή (trophḗ)
16. Ancient Greekτροφῐκός (trophĭkós)
17. English todayhydrogenotrophic

From hydrogen + -o- + -trophic.