Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

barbituric acid
     n : a white crystalline acid derived from pyrimidine; used in
         preparing barbiturate drugs [syn: {malonylurea}]