kingpin

noun5

1. •
   The pin at the centre of the triangle of bowling pins (originally the tallest pin in kayles). Sometimes also the headpin at the apex.
2. •
   (informal, figurative) The most important person in a usually evil undertaking or organization, often a druglord.
3. •
   The axis around which steered wheels pivot; a bolt that holds the axis in place.
4. •
   The pivot or connector between a tractor and trailer in the fifth-wheel coupling of semi-trailer truck.
5. •
   The bolt holding together the truck of a roller skate or skateboard.