Pronunciation: (king'pin"),[key] —n. 1. Bowling. a. headpin.
b. the pin at the center; the number five pin.
2. Informal.the person of chief importance in a corporation, movement, undertaking, etc.
3. Informal.the chief element of any system, plan, or the like.
4. a kingbolt.
5. either of the pins that are a part of the mechanism for turning the front wheels in some automotive steering systems.