Directly from "celer":
* celerity: (noun) swiftness of motion or action; speed.
* celerate: (verb) to accelerate; to move faster.
With "celer" as part of a larger word:
* accelerate: (verb) to increase speed.
* acceleration: (noun) the rate at which velocity changes.
* decelerate: (verb) to decrease speed.
* deceleration: (noun) the rate at which velocity decreases.
Less common, but still related:
* excelerate: (verb) to surpass in speed or excellence.
* celerimeter: (noun) an instrument for measuring speed.
Note that some of these words use "celer" in a slightly modified form, like "accel" or "decel." But they all stem from the same root and share the same meaning of speed.