The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Oxyphenol \Ox`y*phe"nol\, n. (Chem.)
   A phenol, C6H4(OH)2, produced by the distillation of
   catechin; called also oxyphenic acid, and now
   pyrocatechin.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]