Source : Webster's Revised Unabridged Dictionary (1913)

Pyrogallol \Pyr`o*gal"lol\, n. [Pyrogallic + -ol.] (Chem.)
   A phenol metameric with phloroglucin, obtained by the
   distillation of gallic acid as a poisonous white crystalline
   substance having acid properties, and hence called also
   {pyrogallic acid}. It is a strong reducer, and is used as a
   developer in photography and in the production of certain
   dyes.

Source : WordNet®

pyrogallic acid
     n : a toxic white lustrous crystalline phenol used to treat
         certain skin diseases and as a photographic developer
         [syn: {pyrogallol}]