polyrhythmically

The story

1. Proto-Indo-European*pleh₁-
2. Proto-Indo-European*polh₁ús
3. Ancient Greekπολῠ́ς (polŭ́s)
4. Englishpoly-
5. Proto-Indo-European*ser-?
6. Proto-Indo-European*srew-
7. Proto-Indo-European*sru-dʰ-mo-s
8. Proto-Hellenic*hrutʰmós
9. Ancient Greekῥῠθμός (rhŭthmós)
10. Latinrhythmus
11. Englishrhythm
12. Englishpolyrhythm
13. Englishpolyrhythmic
14. Proto-Indo-European*h₂el-
15. Proto-Indo-European*h₂élisder.?
16. Proto-Indo-European*leyg-
17. Proto-Germanic*līką
18. Englishpoly-
19. Ancient Greekῥῠθμός (rhŭthmós)
20. Ancient Greekῥυθμικός (rhuthmikós)
21. Englishrhythmic
22. Englishrhythmical
23. Englishpolyrhythmical
24. English todaypolyrhythmically

From polyrhythmic + -ally, or from polyrhythmical + -ly.