kingbolt

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. 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.

Century Dictionary and Cyclopedia

1. A large bolt connecting the fore part of a carriage with the fore axle. The axle rotates about it as a joint “when the carriage is turned.
2. A large bolt which passes through the truck and body-bolsters and center-plates of a carbody and the center of a truck.
3. Also kiny-pin.
4. n. An iron rod in a roof- or bridge-truss, used in place of a king-post to prevent the inclined members from allowing an increase of the distance between the tie and the compression pieces.

Wiktionary

1. n. The main bolt of a structure, especially the bolt in a motor vehicle that links the chassis to the axle, providing the steering pivot.

GNU Webster's 1913

1. n. A vertical iron bolt, by which the forward axle and wheels of a vehicle or the trucks of a railroad car are connected with the other parts.

WordNet 3.0

1. n. bolt that provides a steering joint in a motor vehicle