a nearly colorless, crystalline acid, (OH)CHCOOH, prepared from tannins, etc. and used in photography and the manufacture of inks, dyes, etc.
Origin:
Fr gallique < galle, gall
See gallic acid in American Heritage Dictionary 4
noun
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.