Rapidity in motion; swiftness; speed; applied most generally to bodies moving on or near the earth; as the celerity of horse or of a fowl. We speak of the velocity of sound or of light, or of a planet in its orbit. This distinction however is not general, nor can the different uses of the two words be precisely defined. We apply celerity rather than velocity to thought; but there seems to be no reason, except usage, why the two words should not be synonymous.'/ .

An affection of motion by which a movable body runs through a given space in a given time.