unpalatalizable

The story

1. Proto-Indo-European*né
2. Proto-Indo-European*n̥-
3. Proto-Germanic*un-
4. Proto-West Germanic*un-
5. Old Englishun-
6. Middle Englishun-
7. Englishun-
8. Proto-Indo-European*pleth₂-?
9. Proto-Indo-European*pel-?
10. Proto-Indo-European*pleh₂-os
11. Latinpalātum
12. Old Frenchpalat
13. Middle Englishpalate
14. Englishpalate
15. Proto-Indo-European*h₂el-
16. Proto-Indo-European*h₂élisder.?
17. Englishpalatal
18. Englishpalatalize
19. Englishpalatalizable
20. English todayunpalatalizable

From un- + palatalizable.