parasitology

The story

1. Proto-Indo-European*per-
2. Proto-Indo-European*preh₂-
3. Proto-Hellenic*pərai
4. Ancient Greekπᾰρᾰ́ (părắ)
5. Ancient Greekσῖτος (sîtos)
6. Ancient Greekπαράσιτος (parásitos)
7. Latinparasītus
8. Middle Frenchparasite
9. Englishparasite
10. Proto-Indo-European*leǵ-
11. Proto-Indo-European*lóǵos
12. Proto-Hellenic*lógos
13. Ancient Greekλόγος (lógos)
14. English todayparasitology

From parasite + -ology.