pyrocatechol

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A biologically important phenol, C₆H₆O₂, having two hydroxyl groups attached to the benzene ring, used in dyeing, tanning, photography, and as an antiseptic.

from The Century Dictionary.

• noun A white crystalline substance, C₆H₄(OH)₂; orthodihydroxybenzene. It occurs in the urine of horses as pyrocatechol-sulphuric acid, and also in human urine and in some plants. It is made by fusing phenol, bromphenol, etc., with caustic potash and by the dry distillation of catechin and many tannins; it melts at 104° C. Also called pyrocatechin, pyrocatechinol, oxyphenic acid; and catechol.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry A dihydric phenol, benzene-1,2-diol, present in some tars.