tetraphosphide

The story

1. Proto-Indo-European*kʷetwóres
2. Proto-Hellenic*kʷétwores
3. Ancient Greekτέσσᾰρες (téssăres)
4. Ancient Greekτετρᾰ- (tetră-)
5. Englishtetra-
6. Proto-Indo-European*bʰeh₂-
7. Proto-Indo-European*bʰéh₂os
8. Proto-Hellenic*pʰáwos
9. Ancient Greekφᾰ́ος (phắos)
10. Ancient Greekφῶς (phôs)
11. Proto-Indo-European*bʰer-
12. Proto-Indo-European*bʰéreti
13. Proto-Hellenic*pʰérō
14. Ancient Greekφέρω (phérō)
15. Ancient Greekφωσφόρος (phōsphóros)
16. Latinphōsphorus
17. Englishphosphorus
18. Englishphospho-
19. Proto-Indo-European*dʰeh₁-
20. Englishphosphide
21. English todaytetraphosphide

From tetra- + phosphide.