undiagnose

The story

1. Proto-Indo-European*h₂ent-
2. Proto-Indo-European*h₂énts
3. Proto-Germanic*anda-
4. Proto-West Germanic*anda-
5. Old Englishand-
6. Old Englishon-
7. Middle Englishon-
8. Englishun-
9. Proto-Indo-European*dwóh₁
10. Proto-Indo-European*trísinflu.
11. Proto-Indo-European*dwís
12. Ancient Greekδιά (diá)
13. Ancient Greekδια- (dia-)
14. Proto-Indo-European*ǵneh₃-
15. Proto-Indo-European*ǵn̥h₃sḱéti
16. Proto-Hellenic*gignṓskō
17. Ancient Greekγῐγνώσκω (gĭgnṓskō)
18. Ancient Greekδῐαγῐγνώσκω (dĭagĭgnṓskō)
19. Ancient Greekδῐᾰ́γνωσῐς (dĭắgnōsĭs)
20. Latindiagnōsis
21. Englishdiagnosisbf.
22. Englishdiagnose
23. English todayundiagnose

From un- + diagnose.