heptaoxide

The story

1. Proto-Afroasiatic*sṗɣ?
2. Proto-Semitic*šabʕ-bor.?
3. Proto-Indo-European*septḿ̥
4. Proto-Hellenic*heptə́
5. Ancient Greekἑπτᾰ́ (heptắ)
6. Englishhepta-
7. Proto-Indo-European*h₂eḱ-der.?
8. Ancient Greekὀξύς (oxús)
9. Proto-Indo-European*ǵenh₁-
10. Proto-Indo-European*ǵénh₁os
11. Proto-Hellenic*génos
12. Ancient Greekγένος (génos)
13. Frenchoxygène
14. Latinacidu
15. Frenchacide
16. Frenchoxide
17. Englishoxide
18. English todayheptaoxide

From hepta- + oxide.