trioxide

The story

1. Proto-Indo-European*tréyes
2. Proto-Indo-European*tri-
3. Proto-Italic*tri-
4. Latintri-
5. Englishtri-
6. Proto-Indo-European*h₂eḱ-der.?
7. Ancient Greekὀξύς (oxús)
8. Proto-Indo-European*ǵenh₁-
9. Proto-Indo-European*ǵénh₁os
10. Proto-Hellenic*génos
11. Ancient Greekγένος (génos)
12. Frenchoxygène
13. Proto-Indo-European*h₂eḱ-
14. Proto-Indo-European*h₂eḱéh₁yeti
15. Proto-Italic*akēō
16. Latinaceō
17. Proto-Indo-European*dʰeh₁-
18. Latinacidu
19. Frenchacide
20. Frenchoxide
21. Englishoxide
22. English todaytrioxide

From tri- + oxide.