quickness of motion; swiftness; speed; celerity; rapidity; as, the velocity of wind; the velocity of a planet or comet in its orbit or course; the velocity of a cannon ball; the velocity of light.-rate of motion; the relation of motion to time, measured by the number of units of space passed over by a moving body or point in a unit of time, usually the number of feet passed over in a second. see the note under speed.