weren't

The story

1. Proto-Indo-European*h₂wes-
2. Proto-Germanic*wēzīn
3. Proto-West Germanic*wāʀīn
4. Old Englishwǣre
5. Old Englishwǣron
6. Old Englishwǣren
7. Middle Englishwere
8. Englishwere
9. Proto-Indo-European*né
10. Proto-Germanic*ne
11. Proto-West Germanic*ne
12. Proto-Indo-European*h₂ey-
13. Proto-Indo-European*h₂óyu
14. Proto-Germanic*aiwaz
15. Proto-West Germanic*aiw
16. Proto-West Germanic*naiw
17. Proto-Indo-European*wekʷ-
18. Proto-Indo-European*wékʷtisder.?
19. Proto-Indo-European*weǵʰ-
20. Proto-Indo-European*wéǵʰtisder.?
21. Proto-Germanic*wihtą
22. Proto-West Germanic*wiht
23. Proto-West Germanic*naiwwiht
24. Old Englishnāwiht
25. Old English*nōht
26. Middle Englishnought
27. Middle Englishnot
28. Englishnot
29. English todayweren't

From were + -n't.