The 'buck' is any inanimate object, usually knife or pencil, which is thrown into a jack pot and temporarily taken by the winner of the pot. Whenever the deal reaches the holder of the 'buck', a new jack pot must be made. [J.W. Keller, "Draw Poker," 1887]Perhaps originally especially a buck-handled knife. The figurative sense of "shift responsibility" is first recorded 1912. Buck private is recorded by 1870s, of uncertain signification.