kingpin

Etymology

king + pin

noun

1. (transport) The axis around which steered wheels pivot; a bolt that holds the axis in place—a kingbolt.
2. (transport) The pivot or connector between a tractor and trailer in the fifth-wheel coupling of semi-trailer truck.
3. (ten-pin bowling">bowling) The pin at the centre of the triangle of bowling">bowling pins (originally the tallest pin in kayles). Sometimes also the headpin at the apex.
4. The most important person in an undertaking or organization.
   The rare salarian females are cloistered on their worlds out of tradition and respect. Powerful female Dalatrasses are dynasts and political kingpins. They determine the political course of their respective regions through shrewd negotiation. 2008, BioWare, Mass Effect, Redwood City: Electronic Arts, →OCLC, PC, scene: Salarians: Culture Codex entry
5. The bolt holding together the truck of a roller skate or skateboard.