fantascience

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. Proto-Indo-European*sek-?
11. Proto-Indo-European*skey-
12. Latinsciō
13. Latinsciēns
14. Latinscientia
15. Old Frenchscience
16. Middle Englishscience
17. Englishscience
18. Ancient Greekφαντάζω (phantázō)
19. Ancient Greekφᾰ́ντᾰσῐς (phắntăsĭs)
20. Ancient Greekφαντασία (phantasía)
21. Latinphantasia
22. Old Frenchfantasie
23. Middle Englishfantasie
24. Englishfantasy
25. Englishscience
26. English todayfantascience

Blend of fantastic + science or fantasy + science.