Where does “wasnae” come from?

wasnae (English) comes from English was, from Middle English was, from Old English wæs, from Proto-Germanic was, from Proto-Indo-European h₂wes- — to dwell, live, reside; to stay, spend the night.

Ancestry of “wasnae”, step by step

wasnae traces back through two separate lines of ancestry.

via English was

StepLanguageWordMeaning
1Englishwasfirst-person singular simple past indicative of...
2Middle EnglishwasFirst and third-person singular past indicative...
3Old Englishwæsfirst/third-person singular preterite of bēon;...
4Proto-Germanicwasfirst/third-person singular past active...
5Proto-Indo-Europeanh₂wes-to dwell, live, reside; to stay, spend the night

via English nae

StepLanguageWordMeaning
1Englishnae
Every word from Proto-Indo-European h₂wes-