millimolar

The story

1. Proto-Indo-European*sem-
2. Proto-Indo-European*sm̥-
3. Proto-Indo-European*smih₂
4. Proto-Indo-European*ǵʰes-
5. Proto-Indo-European*ǵʰéslom
6. Proto-Indo-European*ǵʰéslih₂
7. Proto-Indo-European*smih₂ǵʰéslih₂
8. Proto-Italic*smīɣeslī
9. Latinmīlle
10. Frenchmilli-
11. Englishmilli-
12. Proto-Indo-European*melh₂-
13. Proto-Indo-European*molh₂éh₂
14. Proto-Italic*molā
15. Latinmola
16. Proto-Indo-European*h₂el-
17. Proto-Indo-European*h₂élisder.?
18. Latinmolāris
19. Middle Englishmolar
20. Englishmolar
21. English todaymillimolar

From milli- + molar.