orthophosphate

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*bʰeh₂-
9. Proto-Indo-European*bʰéh₂os
10. Proto-Hellenic*pʰáwos
11. Ancient Greekφᾰ́ος (phắos)
12. Ancient Greekφῶς (phôs)
13. Proto-Indo-European*bʰer-
14. Proto-Indo-European*bʰéreti
15. Proto-Hellenic*pʰérō
16. Ancient Greekφέρω (phérō)
17. Ancient Greekφωσφόρος (phōsphóros)
18. Latinphōsphorus
19. Frenchphosphore
20. Frenchphosphate
21. Englishphosphate
22. English todayorthophosphate

From ortho- + phosphate.