Ox·al·ic a. Chem. Pertaining to, derived from, or contained in, sorrel, or oxalis; specifically, designating an acid found in, and characteristic of, oxalis, and also certain plant of the Buckwheat family.
Oxalic acid Chem., a dibasic acid (HO.CO.CO.OH), existing combined in oxalis as an acid potassium oxalate, and in many plant tissues as the calcium oxalate. It is prepared on a large scale, by the action of fused caustic soda or potash on sawdust, as a white crystalline substance, which has a strong acid taste, and is poisonous in large doses. It is used in dyeing, calico printing, bleaching flax and straw, the preparation of formic acid, and in salts of lemon for removing ink stains, mold, etc.