aseasonal

The story

1. Proto-Indo-European*né
2. Proto-Indo-European*n̥-
3. Proto-Hellenic*ə-
4. Ancient Greekἀ- (a-)
5. Englisha-
6. Proto-Indo-European*h₂éd
7. Proto-Italic*ad
8. Proto-Italic*ad-
9. Latinad-
10. Old Frencha-
11. Frencha-
12. Proto-Indo-European*seh₁-redup.
13. Proto-Indo-European*sísh₁eti
14. Proto-Italic*sizō
15. Latinserō
16. Latinsatiō
17. Old Frenchsaison
18. Frenchsaison
19. Frenchassaisonner
20. Englishseason
21. Proto-Indo-European*h₂el-
22. Proto-Indo-European*h₂élisder.?
23. Englishseasonal
24. English todayaseasonal

From a- + seasonal. Piecewise doublet of unseasonal.