postmaster

The story

1. Proto-Indo-European*h₂ep
2. Proto-Indo-European*h₂epó
3. Proto-Indo-European*h₂pó
4. Proto-Italic*po
5. Proto-Indo-European*teḱ-
6. Proto-Indo-European*tḱéytibf.
7. Proto-Indo-European*tḱey-
8. Proto-Indo-European*tḱinéti
9. Proto-Italic*sinō
10. Proto-Italic*pozinō
11. Latinpōnō
12. Latinposita
13. Italianposta
14. Middle Frenchposte
15. Englishpost
16. Proto-Indo-European*meǵh₂-
17. Proto-Indo-European*meh₂-
18. Proto-Italic*magisteros
19. Latinmagister, magistrum
20. Old Frenchmaistre
21. Latinmagister
22. Old Englishmǣġester
23. Middle Englishmaister
24. Englishmaster
25. English todaypostmaster

From post + master.