inactivable

The story

1. Proto-Indo-European*né
2. Proto-Indo-European*n̥-
3. Proto-Italic*n̥-
4. Latinin-
5. Middle Englishin-
6. Englishin-
7. Proto-Indo-European*h₂eǵ-
8. Proto-Indo-European*h₂éǵeti
9. Proto-Italic*agō
10. Latinagō
11. Ancient Greekἐνεργητικός (energētikós)
12. Latināctīvu
13. Old Frenchactif
14. Middle Englishactyf
15. Englishactive
16. Englishactivate
17. Englishactivable
18. English todayinactivable

From in- + activable.