at

preposition

1. (used to indicate a point or place occupied in space); in, on, or near: to stand at the door; at the bottom of the barrel.
2. (used to indicate a location or position, as in time, on a scale, or in order): at zero; at noon; at age 65; at the end; at the lowest point.
3. (used to indicate presence or location): at home; at hand.
4. (used to indicate amount, degree, or rate): at great speed; at high altitudes.
5. (used to indicate a direction, goal, or objective); toward: Aim at the mark. Look at that.
6. (used to indicate occupation or involvement): at work; at play.
7. (used to indicate a state or condition): at ease; at peace.
8. (used to indicate a cause or source): She was annoyed at his stupidity.
9. (used to indicate a method or manner): He spoke at length.
10. (used to indicate relative quality or value): at one’s best; at cost.