noun
: any of various water-soluble substances obtained in the form of crystals, glasses, powders, or aqueous solutions usually by melting silica with a sodium compound (as sodium carbonate or sodium hydroxide): as
a. or sodium orthosilicate : a corrosive crystalline substance regarded as a salt Na 4 SiO 4 or 2Na 2 O.SiO 2 of orthosilicic acid or as a mixture of sodium metasilicate with sodium hydroxide and used chiefly in heavy-duty cleaning compositions
b. or sodium metasilicate : a crystalline salt Na 2 SiO 3 or Na 2 O.SiO 2 either in the anhydrous or hydrated form used chiefly as a detergent
c. or sodium sesquisilicate : a corrosive crystalline salt regarded as intermediate in composition between sodium orthosilicate and sodium metasilicate and used in heavy-duty cleaning compositions — not used systematically
d. : water glass