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]