subdiagram

The story

1. Proto-Indo-European*upó
2. Proto-Italic*supo
3. Latinsub
4. Latinsub-
5. Englishsub-
6. Proto-Indo-European*dwóh₁
7. Proto-Indo-European*trísinflu.
8. Proto-Indo-European*dwís
9. Ancient Greekδιά (diá)
10. Ancient Greekδῐᾰ- (dĭă-)
11. Proto-Indo-European*gerbʰ-
12. Proto-Hellenic*grə́pʰō
13. Ancient Greekγρᾰ́φω (grắphō)
14. Ancient Greekγρᾰ́μμᾰ (grắmmă)
15. Ancient Greekδιάγραμμα (diágramma)
16. Italiandiagramma
17. Frenchdiagramme
18. Englishdiagram
19. English todaysubdiagram

From sub- + diagram.