nondiagrammatic

The story

1. Proto-Indo-European*né
2. Proto-Germanic*ne
3. Proto-Indo-European*ís?
4. Proto-Indo-European*h₁óynos
5. Proto-Germanic*ainaz
6. Proto-Germanic*nainaz
7. Proto-West Germanic*nain
8. Old Englishnān
9. Middle Englishnon
10. Old Englishnān
11. Old Englishnān-
12. Middle Englishnon-
13. Englishnon-
14. Proto-Indo-European*dwóh₁
15. Proto-Indo-European*trísinflu.
16. Proto-Indo-European*dwís
17. Ancient Greekδιά (diá)
18. Ancient Greekδῐᾰ- (dĭă-)
19. Proto-Indo-European*gerbʰ-
20. Proto-Hellenic*grə́pʰō
21. Ancient Greekγρᾰ́φω (grắphō)
22. Ancient Greekγρᾰ́μμᾰ (grắmmă)
23. Ancient Greekδιάγραμμα (diágramma)
24. Italiandiagramma
25. Frenchdiagramme
26. Englishdiagram
27. Englishdiagrammatic
28. English todaynondiagrammatic

From non- + diagrammatic.