"Speed" can be either a noun or verb: Please see the related link below:
It is called a definition.
The definition of the speed of light in a vacuum is 300,000,000 meters/sec, or 186,000 miles/sec.
Initial speed is the original, beginning speed of an object.
they are fast
Quickness, speed
The speed that an object moves through the air.
Great speed is faster than normal.
"instantaneous speed"
Something that is not restricted to running at one speed.
By definition acceleration is the change in velocity (speed).
The definition of haste is: swiftness of motion; speed; celerity or unnecessarily quick action; thoughtless, rash, or undue speed
Acceleration is when speed increases. Deceleration is when speed decreases.