submicroscopical

The story

1. Proto-Indo-European*upó
2. Proto-Italic*supo
3. Latinsub
4. Latinsub-
5. Englishsub-
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 todaysubmicroscopical

From sub- + microscopical.