self-diagnose

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. Latindiagnōsis
20. Englishdiagnosisbf.
21. Englishdiagnose
22. English todayself-diagnose

From self- + diagnose.