a shoe or some other choke or drag for preventing the wheel of a vehicle from rotating, as when descending a hill.
7.
a runner on the under part of some airplanes, enabling the aircraft to slide along the ground when landing.
8.
an unexpected or uncontrollable sliding on a smooth surface by something not rotating, especially an oblique or wavering veering by a vehicle or its tires: The bus went into a skid on the icy road.
1674, "apply a skid to (a wheel, to keep it from turning)," from skid (n.). Meaning "slide along" first recorded 1838; extended sense of "slip sideways" (on a wet road, etc.) first recorded 1884 (the noun in this sense is attested from 1907). The original notion is of a block