noun
: a phosphate of ammonium made by reaction of ammonia and phosphoric acid: as
a. : the white crystalline primary phosphate NH 4 H 2 PO 4 or sometimes a commercial mixture of this with ammonium sulfate, used chiefly as a fertilizer and as a fire retardant — called also ammonium dihydrogen phosphate, monoammonium phosphate, monobasic ammonium phosphate
b. : the white crystalline secondary phosphate (NH 4 ) 2 HPO 4 similarly used — called also diammonium phosphate, dibasic ammonium phosphate