Barbituric acid \Bar`bi*tu"ric ac"id\ (Chem.) A white, crystalline substance, {CH2(CO.NH)2.CO}, derived from alloxantin, also from malonic acid and urea, and regarded as a substituted urea.
barbituric acid n : a white crystalline acid derived from pyrimidine; used in preparing barbiturate drugs [syn: {malonylurea}]