At is used to show a specific place, time, or point in an activity or process.
It comes from Old English *æt*, which had almost the same meaning, and is related to similar words in other Germanic languages. Its form and sense have stayed remarkably stable over more than a thousand years.
Short words like *at* carry a huge amount of grammar power even though they look tiny and boring. Mastering prepositions often separates fluent speakers from learners, because they encode subtle ways of seeing space, time, and relationships.
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