electrodiagnostically

The story

1. Frenchélectro-
2. Ancient Greekἤλεκτρον (ḗlektron)
3. Latinēlectrum
4. Latinelectro-
5. Englishelectro-
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. Englishelectrodiagnostic
25. Proto-Indo-European*h₂el-
26. Proto-Indo-European*h₂élisder.?
27. Proto-Indo-European*leyg-
28. Proto-Germanic*līką
29. English todayelectrodiagnostically

From electrodiagnostic + -ally. By surface analysis, electro- + diagnostically.