Entry 1 sense Webster, 1913 Mesoxalic · Mes·ox·al·ic · IPA 01 a. Pertaining to, or designating, an acid, CH2O2(CO2H)2, obtained from amido malonic acid. 1. Pertaining to, or designating, an acid, CH2O2(CO2H)2, obtained from amido malonic acid.(Chem.)