I. “+ adjective
Etymology: International Scientific Vocabulary tri- + acid, adjective
1. : able to react with three molecules of a monobasic acid or one of a tribasic acid to form a salt or ester — used especially of bases
2. : containing three hydrogen atoms replaceable by basic atoms or radicals — used especially of acid salts
II. noun
: an acid (as phosphoric acid or citric acid) having three acid hydrogen atoms