The definition of speed is (distance covered) / (time to cover the distance) .
So a unit of speed has to be (a unit of length) / (a unit of time) .
Here are several perfectly fine units of speed:
-- miles per hour
-- feet per second
-- meters per second
-- kilometers per hour
-- inches per second
-- centimeters per minute
-- yards per Century
-- furlongs per fortnight
-- nanometers per microsecond
-- Smoots per week
-- parsecs per millenium
