Source : Webster's Revised Unabridged Dictionary (1913)

Milker \Milk"er\, n.
   1. One who milks; also, a mechanical apparatus for milking
      cows.

   2. A cow or other animal that gives milk.

Source : WordNet®

milker
     n : cattle that are reared for their milk [syn: {dairy cattle},
         {dairy cow}, {milch cow}, {milk cow}, {milcher}]