Source : Webster's Revised Unabridged Dictionary (1913)

Dover's Powder \Do"ver's Pow"der\ [From Dr. Dover, an English
   physician.] (Med.)
   A powder of ipecac and opium, compounded, in the United
   States, with sugar of milk, but in England (as formerly in
   the United States) with sulphate of potash, and in France (as
   in Dr. Dover's original prescription) with nitrate and
   sulphate of potash and licorice. It is an anodyne
   diaphoretic.

Source : WordNet®

Dover's powder
     n : a medicinal powder made essentially of ipecac and opium;
         formerly used to relieve pain and induce perspiration