photochemical

The story

1. Proto-Indo-European*bʰeh₂-
2. Proto-Indo-European*bʰéh₂os
3. Proto-Hellenic*pʰáwos
4. Ancient Greekφᾰ́ος (phắos)
5. Ancient Greekφῶς (phôs)
6. Ancient Greekφωτο- (phōto-)
7. Englishphoto-
8. Proto-Indo-European*ǵʰew-
9. Ancient Greekχῠ́μᾰ (khŭ́mă)
10. Ancient Greekχυμείᾱ (khumeíā)
11. Arabicالْكِيمِيَاء (al-kīmiyāʔ)
12. Medieval Latinalchēmia
13. Ancient Greekχυμείᾱ (khumeíā)influ.
14. New Latinchēmia
15. New Latinchēmicus
16. Proto-Indo-European*h₂el-
17. Proto-Indo-European*h₂élisder.?
18. Englishchemical
19. English todayphotochemical

From photo- + chemical.