fantasticly

The story

1. Proto-Indo-European*bʰeh₂-
2. Proto-Indo-European*bʰh₂nyéti
3. Proto-Hellenic*pʰáňňō
4. Ancient Greekφαίνω (phaínō)
5. Ancient Greekφαντάζω (phantázō)
6. Ancient Greekφανταστικός (phantastikós)
7. Late Latinphantasticus
8. Middle Frenchfantastique
9. Englishfantastic
10. English todayfantasticly

From fantastic + -ly.