magnetofluorescence

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*bʰel-
11. Proto-Indo-European*bʰlewH-
12. Proto-Indo-European*bʰluH-yé-ti?
13. Latinfluō
14. Latinfluor
15. Englishfluor
16. Englishfluorite
17. Middle Low Germanspar
18. Old Englishspærstān
19. Middle Englishsparston
20. Englishsparstonebf.
21. Englishspar
22. Englishfluorspar
23. Englishfluorescence
24. English todaymagnetofluorescence

From magneto- + fluorescence.