Swiftness; 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. In these phrases, velocity is more generally used than celerity. We apply celerity to animals; as, a horse or an ostrich runs with celerity, and a stream runs with rapidity or velocity; but bodies moving in the air or in etherial space, move with greater or less velocity, not celerity. This usage is arbitrary, and perhaps not universal.

In philosophy, velocity is that affection of motion by which a body moves over a certain space in a certain time. Velocity is in direct proportion to the space over which a body moves. Velocity is absolute or relative; absolute, when a body moves over a certain space in a certain time; relative, when it has respect to another moving body. Velocity is also uniform or equal; or it is unequal, that is, retarded or accelerated.