underactivate

The story

1. Proto-Indo-European*h₁én
2. Proto-Indo-European*h₁entér
3. Proto-Indo-European*h₂én
4. Proto-Indo-European*dʰeh₁-?
5. Proto-Indo-European*(H)n̥dʰí
6. Proto-Indo-European*(H)n̥dʰér
7. Proto-Germanic*under
8. Proto-West Germanic*undar
9. Old Englishunder-
10. Middle Englishunder-
11. Englishunder-
12. Proto-Indo-European*h₂eǵ-
13. Proto-Indo-European*h₂éǵeti
14. Proto-Italic*agō
15. Latinagō
16. Ancient Greekἐνεργητικός (energētikós)
17. Latināctīvu
18. Old Frenchactif
19. Middle Englishactyf
20. Englishactive
21. Englishactivate
22. English todayunderactivate

From under- + activate.