unphenomenal

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*bʰeh₂-
9. Proto-Indo-European*bʰh₂nyéti
10. Proto-Hellenic*pʰáňňō
11. Ancient Greekφαίνω (phaínō)
12. Ancient Greekφαινόμενον (phainómenon)
13. Late Latinphaenomenon
14. Englishphenomenon
15. Proto-Indo-European*h₂el-
16. Proto-Indo-European*h₂élisder.?
17. Ancient Greekφαινόμενον (phainómenon)
18. Frenchphénomène
19. Frenchphénoména
20. Englishphenomenal
21. English todayunphenomenal

From un- + phenomenal.