coactivate

The story

1. Proto-Indo-European*ḱe?
2. Proto-Indo-European*ḱóm
3. Proto-Italic*kom
4. Proto-Italic*kom-
5. Latincon-
6. Latinco-
7. Englishco-
8. Proto-Indo-European*h₂eǵ-
9. Proto-Indo-European*h₂éǵeti
10. Proto-Italic*agō
11. Latinagō
12. Ancient Greekἐνεργητικός (energētikós)
13. Latināctīvu
14. Old Frenchactif
15. Middle Englishactyf
16. Englishactive
17. Englishactivate
18. English todaycoactivate

From co- + activate.