unaccentuated

The story

1. Proto-Indo-European*né
2. Proto-Indo-European*n̥-
3. Proto-Germanic*un-
4. Proto-West Germanic*un-
5. Old Englishun-
6. Middle Englishun-
7. Englishun-
8. Proto-Indo-European*h₂éd
9. Proto-Italic*ad
10. Proto-Italic*ad-
11. Latinad-
12. Proto-Indo-European*keh₂n-
13. Proto-Indo-European*kh₂néti
14. Proto-Italic*kanō
15. Latincanō
16. Latinaccinō
17. Ancient Greekπροσῳδῐ́ᾱ (prosōidĭ́ā)
18. Latinaccentus
19. Latinaccentuō
20. Medieval Latinaccentuātus
21. Englishaccentuated
22. English todayunaccentuated

From un- + accentuated.