subdiagnostic

The story

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

From sub- + diagnostic.