nonambiguous

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*h₂ent-
15. Proto-Indo-European*h₂énts?
16. Proto-Indo-European*h₂m̥bʰí
17. Proto-Italic*amβi-
18. Latinambi-
19. Proto-Indo-European*h₂eǵ-
20. Proto-Indo-European*h₂éǵeti
21. Proto-Italic*agō
22. Latinagō
23. Latinambig(ō)
24. Latinambiguu
25. Englishambiguous
26. English todaynonambiguous

From non- + ambiguous.