The Collaborative International Dictionary of English v.0.48:

Bucker \Buck"er\, n. (Mining)
   1. One who bucks ore.
      [1913 Webster]

   2. A broad-headed hammer used in bucking ore.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bucker \Buck"er\, n.
   A horse or mule that bucks.
   [1913 Webster]