semi-automatic

The story

1. Proto-Indo-European*sem-
2. Proto-Indo-European*sēmi
3. Latinsēmi-
4. Englishsemi-
5. Proto-Indo-European*h₂ew
6. Proto-Indo-European*tó-
7. Proto-Hellenic*autós
8. Proto-Indo-European*h₂ew
9. Ancient Greekαὖ (aû)
10. Ancient Greekτόν (tón)
11. Ancient Greekαὐτός (autós)
12. Ancient Greekαὐτο- (auto-)
13. Proto-Indo-European*men-
14. Proto-Indo-European*mn̥tós
15. Proto-Hellenic*mətós
16. Ancient Greekαὐτόμᾰτος (autómătos)
17. Ancient Greekαὐτόμᾰτον (autómăton)
18. Classical Latinautomatum
19. New Latinautomaticus
20. Englishautomatic
21. English todaysemi-automatic

From semi- + automatic.