mysticly

The story

1. Proto-Indo-European*mewH-
2. Proto-Indo-European*mewH-ye-
3. Ancient Greekμῡ́ω (mū́ō)
4. Ancient Greekμῠέω (mŭéō)
5. Ancient Greekμῠ́στης (mŭ́stēs)
6. Ancient Greekμῠστῐκός (mŭstĭkós)
7. Latinmysticus
8. Old Frenchmistique
9. Englishmystic
10. English todaymysticly

From mystic + -ly.