at.

In, near, or in the general vicinity of (a particular place).

Caesar was at Rome.

A climate treaty was signed at Kyoto in 1997.

In, near, or in the general vicinity of (a particular place). Attending (an educational institution).

She's at Oxford University, studying chemistry.

In, near, or in the general vicinity of (a particular place). Working for (a company) or in (a place or situation).

He used to be at Lehman Brothers. Now he's at Merrill Lynch.

'Where does he work?' — 'I think he's still at the solicitors.'

In, near, or in the general vicinity of (a particular place). Indicating distance or direction relative to the speaker.

Target at five miles. Prepare torpedoes.

Look out! UFO at two o'clock!

Present or taking place during (an event).

Was he at the meeting?

There was a big fight at the class reunion.

Indicating time of occurrence, especially an instant of time, or a period of time relatively short in context or from the speaker’s perspective.

at six o’clock; at dawn; at closing time; at the age of twelve; at night; at the moment

Indicating time of occurrence, especially an instant of time, or a period of time relatively short in context or from the speaker’s perspective. (also as at; before dates) On (a particular date).

In the direction of; towards; (often implied to be in a hostile or careless manner).

Don’t just talk at someone; really listen to what they have to say.

Stones were thrown at us, but we couldn't see who did.

Indicating action bearing upon something, especially continued or repeated action.

Don't pick at your food!

My cat keeps scratching at the furniture.

In response or reaction to.

At my request, they agreed to move us to another hotel.

He jumped at the sudden noise.

Occupied in (activity).

men at work; children at play

In a state of.

The two countries are at war.

She is at sixes and sevens with him.

Subject to.

We hope that the event will go ahead, but we are at the whim of the weather.

The city was at the mercy of the occupying forces.

Denotes a price.

3 apples at 2¢ (each)

The offer was at $30,000 before negotiations.

Indicates a position on a scale or in a series.

Sell at $90.

Tiger finished the round at tenth, seven strokes behind the leaders.

In certain phrases, used to indicate the manner in which something happens or is done.

The car came towards me at speed.

He spoke at great length on the topic.

Indicates a specific speed or rate that is maintained by something.

We were cruising along at well over the speed limit of fifty miles per hour.

It is growing at the rate of 3% a year.

Indicates a means or method.

'How was the painting sold?' — 'At auction.'

On the subject of; regarding.

The twins were both bad at chemistry.

He slipped at marksmanship over his extended holiday.

Bothering, irritating, causing discomfort to.

Also used in various other idiomatic combinations: at a pinch, at all, at fault, at pains, at risk, at that, etc.; see the individual entries.

The at sign (@).

Rare form of @; to reply to or talk to someone, either online or face-to-face. (from the practice of targeting a message or reply to someone online by writing @name)

Alternative form of 'at (relative pronoun; reduced form of “that” and/or “what”).

Alternative form of att (Laos currency unit)