Source : Webster's Revised Unabridged Dictionary (1913)

Pyrocatechin \Pyr`o*cat"e*chin\, n. [Pyro- + catechu.] (Chem.)
   A white crystalline substance, {C6H4(OH)2}, of the phenol
   series, found in various plants; -- so called because first
   obtained by distillation of gum catechu. Called also
   {catechol}, {oxyphenol}. etc.

Hydroquinone \Hy`dro*qui"none\, n. [Hydro-, 2 + quinone.]
   (Chem.)
   A white crystalline substance, {C6H4(OH)2}, obtained by the
   reduction of quinone. It is a diacid phenol, resembling, and
   metameric with, pyrocatechin and resorcin. Called also
   {dihydroxy benzene}.