The story
- Proto-Germanic · inherited from*þarat
- Proto-West Germanic · inherited from*þārat
- Old English · inherited fromþǣræt
- Middle English · inherited fromthereat
- English todaythereat
From Middle English thereat, ther-at, þeratte, þerat, from Old English þǣræt, from Proto-West Germanic *þārat, from Proto-Germanic *þarat, equivalent to there + at.
Etymology from Wiktionary, CC BY-SA 4.0.