The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pyrogallol
    n 1: a toxic white lustrous crystalline phenol used to treat
         certain skin diseases and as a photographic developer [syn:
         pyrogallol, pyrogallic acid]