ferromagnetic

The story

1. Old Latin*fersom
2. Latinferrum
3. Englishferro-
4. Old Frenchmagnete
5. Ancient GreekΜάγνης (Mágnēs)
6. Ancient Greekμᾰ́γνης (mắgnēs)
7. Latinmagnēs
8. Middle Englishmagnete
9. Englishmagnet
10. Englishmagnetic
11. English todayferromagnetic

From ferro- + magnetic.