copromicroscopical

The story

1. Proto-Indo-European*ḱekʷ-
2. Proto-Indo-European*ḱókʷr̥
3. Proto-Indo-European*ḱókʷ-ro-s
4. Ancient Greekκόπρος (kópros)
5. Englishcopro-
6. Proto-Indo-European*mey-der.?
7. Ancient Greekμῑκρός (mīkrós)
8. Proto-Indo-European*speḱ-
9. Proto-Indo-European*spéḱyeti
10. Proto-Hellenic*sképt͏̌omai
11. Ancient Greekσκέπτομαι (sképtomai)
12. Ancient Greekσκοπός (skopós)
13. Ancient Greekσκοπέω (skopéō)
14. Latinmīcroscopium
15. Italianmicroscopio
16. Englishmicroscope
17. Proto-Indo-European*h₂el-
18. Proto-Indo-European*h₂élisder.?
19. Englishmicroscopical
20. English todaycopromicroscopical

From copro- + microscopical.