self-diagnostic

The story

1. Proto-Indo-European*swé?
2. Proto-Indo-European*selbʰ-
3. Proto-Germanic*selbaz
4. Old Englishself
5. Old Englishself-
6. Middle Englishself-
7. Englishself-
8. Proto-Indo-European*dwóh₁
9. Proto-Indo-European*trísinflu.
10. Proto-Indo-European*dwís
11. Ancient Greekδιά (diá)
12. Ancient Greekδια- (dia-)
13. Proto-Indo-European*ǵneh₃-
14. Proto-Indo-European*ǵn̥h₃sḱéti
15. Proto-Hellenic*gignṓskō
16. Ancient Greekγῐγνώσκω (gĭgnṓskō)
17. Ancient Greekδῐαγῐγνώσκω (dĭagĭgnṓskō)
18. Ancient Greekδῐᾰ́γνωσῐς (dĭắgnōsĭs)
19. Ancient Greekδῐᾰ- (dĭă-)
20. Proto-Indo-European*ǵneh₃-
21. Proto-Indo-European*ǵneh₃tis
22. Ancient Greekγνῶσις (gnôsis)
23. Ancient Greekγνωστῐκός (gnōstĭkós)
24. Ancient Greekδῐαγνωστῐκός (dĭagnōstĭkós)
25. Englishdiagnostic
26. English todayself-diagnostic

From self- + diagnostic.