acceleration

n. increase of speed

In physics, acceleration is defined as the rate of change of velocity, or, equivalently, as the second derivative of position. It is thus a vector quantity with dimension length/time². In SI units, acceleration is measured in metres/second² (m·s-²). The term "acceleration" generally refers to the change in instantaneous velocity.
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n. acceleration; hurry, quickening, speed up, haste; expedition; hastiness

(n.)
The act of accelerating, or the state of being accelerated; increase of motion or action; as, a falling body moves toward the earth with an acceleration of velocity; -- opposed to retardation.
  

noun
going faster, making something go faster; the nurse noticed an acceleration in the patient's pulse rate