noun
: a brittle white deliquescent solid NaOH that dissolves readily in water to form a strongly alkaline and caustic solution, that is made usually by the electrolysis of common salt or by treating soda ash with hydrated lime, and that is used chiefly in making other chemicals, soap and detergents, rayon and cellulose film, and pulp and paper, in petroleum refining, and in bleaching and mercerizing — called also caustic soda ; compare lye