Speed (noun)

1. The rate at which something moves, operates, or progresses.
2. The rate at which a vehicle is travelling.
3. Rapidity of motion or action.
4. A drug that increases activity in the central nervous system and decreases appetite.
5. The gear or gear ratio used in a vehicle or machine to achieve maximum performance.

Origin:

Middle english spede, from old english spǣd; akin to old high german spuot quickness.

Examples:

1. The speed of light is the fastest known speed in the universe.
2. The speed limit on this road is 50 miles per hour.
3. He works at a speed that is remarkable for his age.
4. She took a speed pill to help her stay awake during the night.
5. He shifted into a higher speed to accelerate the car.