Source : Webster's Revised Unabridged Dictionary (1913)

Soda \So"da\, n. [It., soda, in OIt., ashes used in making
   glass, fr. L. solida, fem. of solidus solid; solida having
   probably been a name of glasswort. See {Solid}.] (Chem.)
   (a) Sodium oxide or hydroxide.
   (b) Popularly, sodium carbonate or bicarbonate.

   {Caustic soda}, sodium hydroxide.

   {Cooking soda}, sodium bicarbonate. [Colloq.]

   {Sal soda}. See {Sodium carbonate}, under {Sodium}.

   {Soda alum} (Min.), a mineral consisting of the hydrous
      sulphate of alumina and soda.

   {Soda ash}, crude sodium carbonate; -- so called because
      formerly obtained from the ashes of sea plants and certain
      other plants, as saltwort ({Salsola}). See under {Sodium}.
      

   {Soda fountain}, an apparatus for drawing soda water, fitted
      with delivery tube, faucets, etc.

   {Soda lye}, a lye consisting essentially of a solution of
      sodium hydroxide, used in soap making.

   {Soda niter}. See {Nitratine}.

   {Soda salts}, salts having sodium for the base; specifically,
      sodium sulphate or Glauber's salts.

   {Soda waste}, the waste material, consisting chiefly of
      calcium hydroxide and sulphide, which accumulates as a
      useless residue or side product in the ordinary Leblanc
      process of soda manufacture; -- called also {alkali
      waste}.

   {Soda water}, originally, a beverage consisting of a weak
      solution of sodium bicarbonate, with some acid to cause
      effervescence; now, in common usage, a beverage consisting
      of water highly charged with carbon dioxide (carbonic
      acid). Fruit sirups, cream, etc., are usually added to
      give flavor. See {Carbonic acid}, under {Carbonic}.

   {Washing soda}, sodium carbonate. [Colloq.]

Source : WordNet®

soda ash
     n : a sodium salt of carbonic acid; used in making soap powders
         and glass and paper [syn: {sodium carbonate}, {washing
         soda}, {sal soda}, {soda}]