• (a.) Having two hydrogen atoms which can be replaced by negative atoms or radicals to form salts; -- said of bases. See Diacid.
Bi·ac'id adjective [ Prefix bi- + acid .] (Chemistry) Having two hydrogen atoms which can be replaced by negative atoms or radicals to form salts; -- said of bases. See Diacid . 
biacid Capable of combining with an acid in two different proportions.