1. Sports.
   1. The innermost or central pin in an arrangement of bowling pins.
   2. See headpin.
2. The most important person or element in an enterprise or system.
3. See kingbolt.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.