nonrigid

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*Hreyǵ-
15. Proto-Italic*rigēō
16. Latinrigeō
17. Proto-Indo-European*dʰeh₁-
18. Latinrigidus
19. Middle Englishrigide
20. Englishrigid
21. English todaynonrigid

From non- + rigid.