The Collaborative International Dictionary of English v.0.48:

Pounder \Pound"er\, n.
   1. One who, or that which, pounds, as a stamp in an ore mill.
      [1913 Webster]

   2. An instrument used for pounding; a pestle.
      [1913 Webster]

   3. A person or thing, so called with reference to a certain
      number of pounds in value, weight, capacity, etc.; as, a
      cannon carrying a twelve-pound ball is called a twelve
      pounder.
      [1913 Webster]

   Note: Before the English reform act of 1867, one who was an
         elector by virtue of paying ten pounds rent was called
         a ten pounder.
         [1913 Webster]

WordNet (r) 3.0 (2006):

pounder
    n 1: (used only in combination) something weighing a given
         number of pounds; "the fisherman caught a 10-pounder";
         "their linemen are all 300-pounders"
    2: a heavy tool of stone or iron (usually with a flat base and a
       handle) that is used to grind and mix material (as grain or
       drugs or pigments) against a slab of stone [syn: pestle,
       muller, pounder]