The Collaborative International Dictionary of English v.0.48:

Pyrogallic \Pyr`o*gal"lic\, a. [Pyro- + gallic.] (Chem.)
   Pertaining to, derived from, or designating, an acid called
   pyrogallol. See Pyrogallol.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pyrogallic
    adj 1: of or relating to pyrogallol