multiethnic

The story

1. Proto-Indo-European*mel-
2. Proto-Indo-European*ml̥tós?
3. Proto-Italic*moltos
4. Latinmultus
5. Latinmultī
6. Middle Englishmulti-
7. Englishmulti-
8. Proto-Indo-European*swé
9. Proto-Indo-European*dʰeh₁-
10. Proto-Indo-European*swe-dʰh₁-
11. Proto-Hellenic*séswōtʰa
12. Ancient Greekἔθω (éthō)
13. Ancient Greekἔθνος (éthnos)
14. Ancient Greekἐθνικός (ethnikós)
15. Latinethnicus
16. Middle Englishethnik
17. Englishethnic
18. English todaymultiethnic

From multi- + ethnic.