Acceleration/əkˌseləˈreɪʃn/ Definition 1 of 4Pro Tip 1/3Physical Movement Refers to something gaining speed, often used with machines or athletes. The sprinter's acceleration during the race was astounding. Pro Tip 2/3Impressive Performance Expresses admiration when an object or person speeds up quickly. The motorcycle's acceleration is so impressive that it leaves everyone behind. Pro Tip 3/3Negative Usage Can indicate slowing down, opposite of speeding up, depending on context. When the driver hit the brakes, the car's negative acceleration was jarring.