noun
1. : any of several crystalline sodium salts NaPO 3 or (NaPO 3 ) n of a metaphosphoric acid: as
a. : the water-soluble cyclic trimetaphosphate (NaPO 3 ) 3 or NaPO 3 I
b. : sodium Kurrol's salt NaPO 3 IV
2.
a. : a water-soluble sodium phosphate glass having the composition of a sodium metaphosphate — called also sodium (1:1) phosphate ; compare sodium hexametaphosphate
b. : sodium phosphate glass