Source : Webster's Revised Unabridged Dictionary (1913)

Hack \Hack\, a.
   Hackneyed; hired; mercenary. --Wakefield.

   {Hack writer}, a hack; one who writes for hire. ``A vulgar
      hack writer.'' --Macaulay.

Source : WordNet®

hack writer
     n : a mediocre and disdained writer [syn: {hack}, {literary hack}]