The definition of a kingbolt is a main bolt that connects the front axle of a vehicle with the body.
An example of kingbolt is how railroad cars are connected together.
any main bolt; esp., one that acts as a vertical pivot for a turning vehicle, as that connecting the front axle of a wagon, etc., or the truck of a railroad car, with the body
A vertical bolt that joins the body of a wagon or other vehicle to its front axle and usually acts as a pivot. Also called kingpin.