underdiagnose

The story

1. Proto-Indo-European*h₁én
2. Proto-Indo-European*h₁entér
3. Proto-Indo-European*h₂én
4. Proto-Indo-European*dʰeh₁-?
5. Proto-Indo-European*(H)n̥dʰí
6. Proto-Indo-European*(H)n̥dʰér
7. Proto-Germanic*under
8. Proto-West Germanic*undar
9. Old Englishunder-
10. Middle Englishunder-
11. Englishunder-
12. Proto-Indo-European*dwóh₁
13. Proto-Indo-European*trísinflu.
14. Proto-Indo-European*dwís
15. Ancient Greekδιά (diá)
16. Ancient Greekδια- (dia-)
17. Proto-Indo-European*ǵneh₃-
18. Proto-Indo-European*ǵn̥h₃sḱéti
19. Proto-Hellenic*gignṓskō
20. Ancient Greekγῐγνώσκω (gĭgnṓskō)
21. Ancient Greekδῐαγῐγνώσκω (dĭagĭgnṓskō)
22. Ancient Greekδῐᾰ́γνωσῐς (dĭắgnōsĭs)
23. Latindiagnōsis
24. Englishdiagnosisbf.
25. Englishdiagnose
26. English todayunderdiagnose

From under- + diagnose.