autoimmune

The story

1. Proto-Indo-European*h₂ew
2. Proto-Indo-European*tó-
3. Proto-Hellenic*autós
4. Proto-Indo-European*h₂ew
5. Ancient Greekαὖ (aû)
6. Ancient Greekτόν (tón)
7. Ancient Greekαὐτός (autós)
8. Ancient Greekαὐτο- (auto-)
9. Englishauto-
10. Proto-Indo-European*mey-
11. Proto-Indo-European*moy-nós
12. Proto-Italic*moinos
13. Latinmūnus
14. Proto-Indo-European*né
15. Proto-Indo-European*n̥-
16. Proto-Italic*n̥-
17. Latinin-
18. Latinin- -is
19. Latinimmūnis
20. Middle Frenchimmun
21. Englishimmune
22. English todayautoimmune

From auto- + immune.