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}.