noun
1. : an orthophosphate of sodium known in both anyhydrous and hydrated crystalline forms:
a. : the primary phosphate NaH 2 PO 4 that with the secondary phosphate constitutes the principal buffer system of the urine and that is used chiefly in buffer compositions (as in acid cleaning compositions) — called also monobasic sodium phosphate, monosodium phosphate, sodium acid phosphate, sodium dihydrogen phosphate
b. : the secondary phosphate Na 2 HPO 4 that is used chiefly in water treatment for precipitating polyvalent metals, in cleaning compositions, in process cheeses, in ceramic glazes and enamels, in the textile industry, and in medicine as a laxative and antacid — called also dibasic sodium phosphate, disodium hydrogen phosphate, disodium phosphate
c. : the tertiary phosphate Na 3 PO 4 that is used chiefly in cleaning compositions and in water treatment — called also tribasic sodium phosphate, trisodium phosphate
2. : a phosphate of sodium that is not an orthophosphate — compare sodium metaphosphate , sodium pyrophosphate , sodium tripolyphosphate