acceleration

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act of accelerating.
2. n. The process of being accelerated.
3. n. Physics The rate of change of velocity with respect to time.

Century Dictionary and Cyclopedia

1. n. The act of accelerating, or the state of being accelerated: as— A gradual increase of velocity.
2. n. In mech., the rate of change of the velocity of a moving body; that is, the increment of velocity (in any direction) in the unit of time which would result were the rate of change to continue uniform for that length of time. The acceleration is said to be uniform if the body gains the same velocity in any constant direction in equal successive portions of time, no matter how small these portions may be taken. A constant force produces uniform acceleration in all cases; but it is sometimes convenient to substitute for some of the forces fictitious “constraints.” Thus, gravity (which near the earth's surface is sensibly a constant force) gives a falling body uniformly accelerated motion when the effect of the atmospheric resistance is eliminated; in this case the increment of velocity in each second, which is a little more than 32 feet, is called the acceleration of gravity, and in mechanical formulas is denoted by the letter g. When the velocity of a moving body continually diminishes, the acceleration is termed minus or negative, and the motion is said to be retarded; this is illustrated by the case of a ball thrown upward, the upward component of the velocity of which diminishes at the rate of 32 feet a second. Similarly, the force of friction which resists the motion of a sliding body is said to give it minus or negative acceleration.
3. n. The shortening of the time between the present and the happening of any future event; specifically, in law, the shortening of the time before the vesting of a person with the possession of an expected interest. In physiology and pathology, increased activity of the functions of the body, particularly of the circulation of the fluids.
4. n. In biology, the supposed acquisition of new characters by adults, and their inheritance by descendants at earlier and earlier stages of their life; tachygenesis (which see).

Wiktionary

1. n. uncountable The act of accelerating, or the state of being accelerated; increase of motion or action; as opposed to retardation or deceleration.
2. n. countable The amount by which a speed or velocity increases (and so a scalar quantity or a vector quantity).
3. n. physics The change of velocity with respect to time (can include deceleration or changing direction).

GNU Webster's 1913

1. n. The act of accelerating, or the state of being accelerated; increase of motion or action; ; -- opposed to retardation.
2. n. See Priming of the tides, under Priming.

WordNet 3.0

1. n. the act of accelerating; increasing the speed
2. n. (physics) a rate of increase of velocity
3. n. an increase in rate of change