gearwheel

The story

1. Proto-Indo-European*ḱe?
2. Proto-Indo-European*ḱóm
3. Proto-Germanic*ga-
4. Proto-Indo-European*h₂er-
5. Proto-Indo-European*h₃er-
6. Proto-Germanic*arwaz
7. Proto-Germanic*garwaz
8. Proto-Germanic*garwijaną
9. Old Norsegervi
10. Middle Englishgere
11. Englishgear
12. Proto-Indo-European*kʷelh₁-redup.
13. Proto-Indo-European*kʷekʷléh₂
14. Proto-Germanic*hweulō
15. Old Englishhwēol
16. Middle Englishwhel
17. Englishwheel
18. English todaygearwheel

From gear + wheel.