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.
c.1600, "beam or plank on which something rests," probably from a Scandinavian source akin to O.N. skið "stick of wood" (see ski). A skid as something used to facilitate downhill motion (cf. skid row) led to fig. phrases such as hit the skids "go into rapid decline" (1920).
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
of wood for stopping a wheel; the modern senses are from the notion of a wheel slipping when blocked from revolving.