compartmentalisation

The story

1. Proto-Indo-European*ḱe?
2. Proto-Indo-European*ḱóm
3. Proto-Italic*kom
4. Proto-Italic*kom-
5. Latincom-
6. Proto-Indo-European*perh₃-
7. Proto-Indo-European*pérh₃tis?
8. Proto-Italic*partis
9. Latinpars
10. Latinpartiō
11. Latinpartior
12. Latincompartīrī
13. Italiancompartire
14. Italiancompartimento
15. Middle Frenchcompartiment
16. Englishcompartment
17. Proto-Indo-European*h₂el-
18. Proto-Indo-European*h₂élisder.?
19. Englishcompartmental
20. Englishcompartmentalise
21. English todaycompartmentalisation

From compartmentalise + -ation.