Source : Webster's Revised Unabridged Dictionary (1913)

Mill \Mill\, v. t. [imp. & p. p. {Milled}; p. pr. & vb. n.
   {Milling}.] [See {Mill}, n., and cf. {Muller}.]
   1. To reduce to fine particles, or to small pieces, in a
      mill; to grind; to comminute.

   2. To shape, finish, or transform by passing through a
      machine; specifically, to shape or dress, as metal, by
      means of a rotary cutter.

   3. To make a raised border around the edges of, or to cut
      fine grooves or indentations across the edges of, as of a
      coin, or a screw head; also, to stamp in a coining press;
      to coin.

   4. To pass through a fulling mill; to full, as cloth.

   5. To beat with the fists. [Cant] --Thackeray.

   6. To roll into bars, as steel.

   {To mill chocolate}, to make it frothy, as by churning.

Milling \Mill"ing\, n.
   The act or employment of grinding or passing through a mill;
   the process of fulling; the process of making a raised or
   intented edge upon coin, etc.; the process of dressing
   surfaces of various shapes with rotary cutters. See {Mill}.

   {High milling}, milling in which grain is reduced to flour by
      a succession of crackings, or of slight and partial
      crushings, alternately with sifting and sorting the
      product.

   {Low milling}, milling in which the reduction is effected in
      a single crushing or grinding.

   {Milling cutter}, a fluted, sharp-edged rotary cutter for
      dressing surfaces, as of metal, of various shapes.

   {Milling machine}, a machine tool for dressing surfaces by
      rotary cutters.

   {Milling tool}, a roller with indented edge or surface, for
      producing like indentations in metal by rolling pressure,
      as in turning; a knurling tool; a milling cutter.

Source : WordNet®

milling
     n : corrugated edge of a coin