ereyesterday

The story

1. Proto-Indo-European*h₂ey-
2. Proto-Indo-European*h₂éyeri
3. Proto-Germanic*airi
4. Proto-Germanic*airiz
5. Old Englishǣr
6. Middle Englisher
7. Englishere
8. Proto-Indo-European*dʰǵʰyés
9. Proto-Indo-European*dʰǵʰyésteros
10. Proto-Germanic*gesteraz
11. Proto-Germanic*gesteran
12. Proto-West Germanic*gesteran
13. Old Englishġiestran
14. Proto-Indo-European*dʰegʷʰ-?
15. Proto-Germanic*dagaz
16. Proto-West Germanic*dag
17. Old Englishdæġ
18. Old Englishġiestrandæġ
19. Middle Englishyesterday
20. Englishyesterday
21. English todayereyesterday

From ere (“before”, preposition) + yesterday. Compare French avant-hier, Dutch eergisteren, German vorgestern, Polish przedwczoraj, Swedish förrgår or Danish forgårs.