parasitically

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. Englishparasitic
11. Proto-Indo-European*h₂el-
12. Proto-Indo-European*h₂élisder.?
13. Proto-Indo-European*leyg-
14. Proto-Germanic*līką
15. English todayparasitically

From parasitic + -ally.