nonactivatable

The story

1. Proto-Indo-European*né
2. Proto-Germanic*ne
3. Proto-Indo-European*ís?
4. Proto-Indo-European*h₁óynos
5. Proto-Germanic*ainaz
6. Proto-Germanic*nainaz
7. Proto-West Germanic*nain
8. Old Englishnān
9. Middle Englishnon
10. Old Englishnān
11. Old Englishnān-
12. Middle Englishnon-
13. Englishnon-
14. Proto-Indo-European*h₂eǵ-
15. Proto-Indo-European*h₂éǵeti
16. Proto-Italic*agō
17. Latinagō
18. Ancient Greekἐνεργητικός (energētikós)
19. Latināctīvu
20. Old Frenchactif
21. Middle Englishactyf
22. Englishactive
23. Englishactivate
24. Englishactivatable
25. English todaynonactivatable

From non- + activatable.