undifferentially

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*dwóh₁
9. Proto-Indo-European*trísinflu.
10. Proto-Indo-European*d(w)is-
11. Proto-Italic*dis-
12. Latindis-
13. Proto-Indo-European*bʰer-
14. Proto-Indo-European*bʰéreti
15. Proto-Italic*ferō
16. Latinferō
17. Latindifferō
18. Latindifferēns
19. Latindifferentia
20. Proto-Indo-European*h₂el-
21. Proto-Indo-European*h₂élisder.?
22. Latindifferentiāli
23. Englishdifferential
24. Englishdifferentially
25. English todayundifferentially

From un- + differentially.