(1):

(v. t.) To hasten, as the occurence of an event; as, to accelerate our departure.

(2):

(v. t.) To quicken the natural or ordinary progression or process of; as, to accelerate the growth of a plant, the increase of wealth, etc.

(3):

(v. t.) To cause to move faster; to quicken the motion of; to add to the speed of; - opposed to retard.