quasidifferentiable

The story

1. Proto-Indo-European*kʷ-
2. Proto-Indo-European*kʷís
3. Proto-Italic*kʷis
4. Proto-Indo-European*kʷ-
5. Proto-Indo-European*kʷos
6. Proto-Italic*kʷoi
7. Latinquam
8. Proto-Indo-European*só
9. Proto-Italic*sei
10. Latinsī
11. Latinquasī̆
12. Englishquasi-
13. Proto-Indo-European*dwóh₁
14. Proto-Indo-European*trísinflu.
15. Proto-Indo-European*d(w)is-
16. Proto-Italic*dis-
17. Latindis-
18. Proto-Indo-European*bʰer-
19. Proto-Indo-European*bʰéreti
20. Proto-Italic*ferō
21. Latinferō
22. Latindifferō
23. Latindifferēns
24. Latindifferentia
25. New Latindifferentiō
26. New Latindifferentiātus
27. Englishdifferentiate
28. Englishdifferentiable
29. English todayquasidifferentiable

From quasi- + differentiable.