diagnostically

The story

1. Proto-Indo-European*dwóh₁
2. Proto-Indo-European*trísinflu.
3. Proto-Indo-European*dwís
4. Ancient Greekδιά (diá)
5. Ancient Greekδια- (dia-)
6. Proto-Indo-European*ǵneh₃-
7. Proto-Indo-European*ǵn̥h₃sḱéti
8. Proto-Hellenic*gignṓskō
9. Ancient Greekγῐγνώσκω (gĭgnṓskō)
10. Ancient Greekδῐαγῐγνώσκω (dĭagĭgnṓskō)
11. Ancient Greekδῐᾰ́γνωσῐς (dĭắgnōsĭs)
12. Ancient Greekδῐᾰ- (dĭă-)
13. Proto-Indo-European*ǵneh₃-
14. Proto-Indo-European*ǵneh₃tis
15. Ancient Greekγνῶσις (gnôsis)
16. Ancient Greekγνωστῐκός (gnōstĭkós)
17. Ancient Greekδῐαγνωστῐκός (dĭagnōstĭkós)
18. Englishdiagnostic
19. Proto-Indo-European*h₂el-
20. Proto-Indo-European*h₂élisder.?
21. Proto-Indo-European*leyg-
22. Proto-Germanic*līką
23. English todaydiagnostically

From diagnostic + -ally.