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.]

Caustic \Caus"tic\, Caustical \Caus"tic*al\, a. [L. caustucs,
   Ge. ?, fr. ? to burn. Cf. {Calm}, {Ink}.]
   1. Capable of destroying the texture of anything or eating
      away its substance by chemical action; burning; corrosive;
      searing.

   2. Severe; satirical; sharp; as, a caustic remark.

   {Caustic curve} (Optics), a curve to which the ray of light,
      reflected or refracted by another curve, are tangents, the
      reflecting or refracting curve and the luminous point
      being in one plane.

   {Caustic lime}. See under {Lime}.

   {Caustic potash}, {Caustic soda} (Chem.), the solid
      hydroxides potash, {KOH}, and soda, {NaOH}, or solutions
      of the same.

   {Caustic silver}, nitrate of silver, lunar caustic.

   {Caustic surface} (Optics), a surface to which rays reflected
      or refracted by another surface are tangents. Caustic
      curves and surfaces are called catacaustic when formed by
      reflection, and diacaustic when formed by refraction.

   Syn: Stinging; cutting; pungent; searching.

Source : WordNet®

caustic soda
     n : a strongly alkaline caustic used in manufacturing soap and
         paper and aluminum and various sodium compounds [syn: {sodium
         hydroxide}]