| a white or yellowish, crystalline, sparingly water-soluble solid, C7H6O5, obtained from nutgalls, used chiefly in tanning and in ink dyes. |
gal·lic acid  (gāl'ĭk, gô'lĭk)  n. A colorless crystalline compound, C7H6O5, derived from tannin and used as a tanning agent, as an ink dye, and in photography and the manufacture of paper. [French acide gallique, from galle, plant gall; see gall3.] |
gallic acid
substance occurring in many plants, either in the free state or combined as gallotannin. It is present to the extent of 40-60 percent combined as gallotannic acid in tara (any of various plants of the genus Caesalpinia) and in Aleppo and Chinese galls (swellings of plant tissue), from which it is obtained commercially by the action of acids or alkalies. An Aleppo gall has a spherical shape, is hard and brittle, and is about the size of a hickory nut; it is produced on oak twigs by a gall wasp (Cynips tinctoria). A Chinese gall is produced by insects on Asian sumac (Rhus semialata).
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