1. prep. In, near, or in the general vicinity of a particular place.
Caesar was at Rome; at the corner of Fourth Street and Vine; at Jim’s house
2. prep. (indicating time) (Indicating occurrence in an instant of time or a period of time relatively short in context or from the speaker's perspective.)
at six o’clock; at closing time; at night.
3. prep. In the direction of (often in an unfocused or uncaring manner).