diaperbrain

The story

1. Proto-Indo-European*dwóh₁
2. Proto-Indo-European*trísinflu.
3. Proto-Indo-European*dwís
4. Ancient Greekδιά (diá)
5. Ancient Greekδια- (dia-)
6. Proto-Indo-European*h₂esp-der.?
7. Latinasper
8. Ancient Greekἄσπρος (áspros)
9. Medieval Greekδίασπρος (díaspros)
10. Medieval Latindiaspra
11. Old Frenchdyapre
12. Middle Englishdyaper
13. Englishdiaper
14. Proto-Indo-European*mregʰ-
15. Proto-Indo-European*mrógʰ-n̥ ~ *mrégʰ-n̥-s
16. Proto-Germanic*bragną
17. Proto-West Germanic*bragn
18. Old Englishbræġn
19. Middle Englishbrayn
20. Englishbrain
21. English todaydiaperbrain

From diaper (“an absorbent garment”) + brain (“mind”).