undermotivated

The story

1. Proto-Indo-European*h₁én
2. Proto-Indo-European*h₁entér
3. Proto-Indo-European*h₂én
4. Proto-Indo-European*dʰeh₁-?
5. Proto-Indo-European*(H)n̥dʰí
6. Proto-Indo-European*(H)n̥dʰér
7. Proto-Germanic*under
8. Proto-West Germanic*undar
9. Old Englishunder-
10. Middle Englishunder-
11. Englishunder-
12. Anglo-Normanmotif
13. Middle Frenchmotif
14. Proto-Indo-European*m(y)ewh₁-
15. Proto-Indo-European*m(y)owh₁éyeti
16. Proto-Italic*moweō
17. Latinmoveō
18. Latinmōtus
19. Late Latinmōtīvum
20. Middle Englishmotif
21. Englishmotive
22. Englishmotivated
23. English todayundermotivated

From under- + motivated.