Kingpin

[king-pin] /ˈkɪŋˌpɪn/

noun
1.
Bowling.

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.
/ˈkɪŋˌpɪn/
noun
1.
the most important person in an organization
2.
the crucial or most important feature of a theory, argument, etc
3.
Also called (Brit) swivel pin. a pivot pin that provides a steering joint in a motor vehicle by securing the stub axle to the axle beam
4.
(tenpin bowling) the front pin in the triangular arrangement of the ten pins
5.
(in ninepins) the central pin in the diamond pattern of the nine pins
n.

also king-pin, 1801 as the name of the large pin in the game of kayles (similar to bowls except a club or stick was thrown instead of a ball; cf. “Games, Gaming and Gamesters’ Laws,” Frederick Brandt, London, 1871), from king with a sense of “chief” + pin (n.). The modern use is mainly figurative and is perhaps from the word’s use as another name for the king-bolt (itself from 1825) in a machinery, though the figurative use is attested earlier (1867) than the literal.