magnetohydrodynamic

The story

1. Ancient GreekΜάγνης (Mágnēs)
2. Ancient Greekμᾰ́γνης (mắgnēs)
3. Old Frenchmagnete
4. Ancient Greekμᾰ́γνης (mắgnēs)
5. Latinmagnēs
6. Middle Englishmagnete
7. Englishmagnet
8. Englishmagnet-
9. Englishmagneto-
10. Proto-Indo-European*wed-
11. Proto-Indo-European*wódr̥
12. Proto-Hellenic*údōr
13. Ancient Greekῡ̆̔́δωρ (hū̆́dōr)
14. Ancient Greekῠ̔δρο- (hŭdro-)
15. Englishhydro-
16. Proto-Indo-European*dewh₂-
17. Proto-Hellenic*dunamai
18. Ancient Greekδῠ́νᾰμαι (dŭ́nămai)
19. Ancient Greekδύναμις (dúnamis)
20. Ancient Greekδυναμικός (dunamikós)
21. Frenchdynamique
22. Englishdynamic
23. English todaymagnetohydrodynamic

From magneto- + hydro- + dynamic.