phosphonium

The story

1. Proto-Indo-European*bʰeh₂-
2. Proto-Indo-European*bʰéh₂os
3. Proto-Hellenic*pʰáwos
4. Ancient Greekφᾰ́ος (phắos)
5. Ancient Greekφῶς (phôs)
6. Proto-Indo-European*bʰer-
7. Proto-Indo-European*bʰéreti
8. Proto-Hellenic*pʰérō
9. Ancient Greekφέρω (phérō)
10. Ancient Greekφωσφόρος (phōsphóros)
11. Latinphōsphorus
12. Englishphosphorusclip.
13. Englishphosph-
14. New Latinammōnium
15. Englishammonium
16. Englishonium
17. English todayphosphonium

From phosph- + -onium.