undertone

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. Proto-Indo-European*ten-
13. Proto-Indo-European*tónos
14. Proto-Hellenic*tónos
15. Ancient Greekτόνος (tónos)
16. Latintonus
17. Middle Englishtone
18. Englishtone
19. English todayundertone

From under- + tone.