1 used to show a point in space where someone or something is, or where an event is happening: We'll meet at my house. | a huge queue at the bus stop. | They sat down at a corner table. | at Jack's/Sue's etc (=at Jack's house, Sue's house etc): Pete's round at Mel's. | at the doctor's/the bank/the airport etc (=at a place you go to for a particular purpose): Guess who I met at the dentist's?2 at a party/club/funeral etc at an event while it is taking place: I met my wife at a disco. | They're all out at the cinema.3 at school/work etc regularly going to school, work etc: Is Jessica still at school? (=does she go to school regularly)4 at lunch/dinner etc eating your lunch, dinner etc: I'm sorry, Pam's at lunch just now.5 used to show an exact time: The film starts at 8 o'clock. | at the moment (=now): We're really busy at the moment.6 used to show a particular period of time during which something happens: My husband often works at night. | We like to go to Midnight Mass at Christmas.7 used to show the person or thing that an action is directed or aimed at: Protesters threw rotten eggs at the speakers. | Jake shot at the deer but missed. | Look at that! | Stop shouting at the kids all the time.8 used to show the thing that caused an action or feeling: The children all laughed at his jokes. | I'm surprised at you! | Dad got really mad at me for scratching the car.9 used to show the subject or activity that you are considering when making a judgment about someone's ability: Barbara's getting on really well at her new job. | Rosa's a genius at chemistry. | good/bad etc at (doing) sth: Luis was always good at maths. | Matt's bad at handling people.10 used to show a continuous state or activity: two nations at war | Many children are still at risk from neglect or abuse. | Granny's at peace now (=dead) | at large (=if someone or something dangerous is at large they are in a particular area and may harm or kill someone): rumours of a black panther at large11 used to show a price, rate, level, age, speed etc: old books selling at 10 cents each | The house was sold at a price of $250,000. | You should have more sense at your age. | The car was going at about 50 mph. | Amanda rode off at a gallop.12 at least/worst/most etc the least, worst etc thing possible: John has to practise for at least half an hour every day. | At worst, up to 50% of the population could be affected. | at the very least/most/worst etc: That car's worth $250 at the very most. | at its/her/their best etc: The garden is at its best in June. | This was Sampras at his most powerful.13 used to show that you are trying to do something but are not succeeding or completing it: George was just picking at his food. | Sarah took another sip at her wine. | I clutched at the rope but missed.14 at sb's invitation/command because someone asks or orders you to do something: Rachel attended the dinner at the chairman's command.15 at thata) also or besides: It's a new idea, and a good one, at that.b) after something happens or as a result of it; then: Tess called him a liar and at that he stormed out of the room.-see also: leave it at that leave 1 (12)16 at a time at the same time: Ben was putting chocolates in his mouth two at a time.17 where it's at informal used to describe a place or activity that is very popular, exciting, and fashionable: This Hacienda Club is where it's at.-see also (not) at all all 3
Longman dictionary of contemporary English. 2004.