† 1.  The tallest (central) pin in the game of kayles.

1

1801.  Strutt, Sports & Past., III. vii. 239. One of them … is taller than the rest, and this, I presume, was the king-pin.

2

  2.  = KING-BOLT. Hence fig., that which holds together any complex system or arrangement.

3

1895.  Libr. Jrnl. (U.S.), June, 202. Mr. Vinton … believed cataloging to be the king-pin of the library system.

4

1898.  R. Kipling, Fleet in Being, vi. 76. The newer generation, bred to pole-masts, know that he is the king-pin of their system.

5