Source : Webster's Revised Unabridged Dictionary (1913)

Salt \Salt\, n. [AS. sealt; akin to OS. & OFries. salt, D. zout,
   G. salz, Icel., Sw., & Dan. salt, L. sal, Gr. ?, Russ. sole,
   Ir. & Gael. salann, W. halen, of unknown origin. Cf. {Sal},
   {Salad}, {Salary}, {Saline}, {Sauce}, {Sausage}.]
   1. The chloride of sodium, a substance used for seasoning
      food, for the preservation of meat, etc. It is found
      native in the earth, and is also produced, by evaporation
      and crystallization, from sea water and other water
      impregnated with saline particles.

   2. Hence, flavor; taste; savor; smack; seasoning.

            Though we are justices and doctors and churchmen . .
            . we have some salt of our youth in us. --Shak.

   3. Hence, also, piquancy; wit; sense; as, Attic salt.

   4. A dish for salt at table; a saltcellar.

            I out and bought some things; among others, a dozen
            of silver salts.                      --Pepys.

   5. A sailor; -- usually qualified by old. [Colloq.]

            Around the door are generally to be seen, laughing
            and gossiping, clusters of old salts. --Hawthorne.

   6. (Chem.) The neutral compound formed by the union of an
      acid and a base; thus, sulphuric acid and iron form the
      salt sulphate of iron or green vitriol.

   Note: Except in case of ammonium salts, accurately speaking,
         it is the acid radical which unites with the base or
         basic radical, with the elimination of hydrogen, of
         water, or of analogous compounds as side products. In
         the case of diacid and triacid bases, and of dibasic
         and tribasic acids, the mutual neutralization may vary
         in degree, producing respectively basic, neutral, or
         acid salts. See Phrases below.

   7. Fig.: That which preserves from corruption or error; that
      which purifies; a corrective; an antiseptic; also, an
      allowance or deduction; as, his statements must be taken
      with a grain of salt.

            Ye are the salt of the earth.         --Matt. v. 13.

   8. pl. Any mineral salt used as an aperient or cathartic,
      especially Epsom salts, Rochelle salt, or Glauber's salt.

   9. pl. Marshes flooded by the tide. [Prov. Eng.]

   {Above the salt}, {Below the salt}, phrases which have
      survived the old custom, in the houses of people of rank,
      of placing a large saltcellar near the middle of a long
      table, the places above which were assigned to the guests
      of distinction, and those below to dependents, inferiors,
      and poor relations. See {Saltfoot}.

            His fashion is not to take knowledge of him that is
            beneath him in clothes. He never drinks below the
            salt.                                 --B. Jonson.

   {Acid salt} (Chem.)
      (a) A salt derived from an acid which has several
          replaceable hydrogen atoms which are only partially
          exchanged for metallic atoms or basic radicals; as,
          acid potassium sulphate is an acid salt.
      (b) A salt, whatever its constitution, which merely gives
          an acid reaction; thus, copper sulphate, which is
          composed of a strong acid united with a weak base, is
          an acid salt in this sense, though theoretically it is
          a neutral salt.

   {Alkaline salt} (Chem.), a salt which gives an alkaline
      reaction, as sodium carbonate.

   {Amphid salt} (Old Chem.), a salt of the oxy type, formerly
      regarded as composed of two oxides, an acid and a basic
      oxide. [Obsolescent]

   {Basic salt} (Chem.)
      (a) A salt which contains more of the basic constituent
          than is required to neutralize the acid.
      (b) An alkaline salt.

   {Binary salt} (Chem.), a salt of the oxy type conveniently
      regarded as composed of two ingredients (analogously to a
      haloid salt), viz., a metal and an acid radical.

   {Double salt} (Chem.), a salt regarded as formed by the union
      of two distinct salts, as common alum, potassium aluminium
      sulphate. See under {Double}.

   {Epsom salts}. See in the Vocabulary.

   {Essential salt} (Old Chem.), a salt obtained by
      crystallizing plant juices.

   {Ethereal salt}. (Chem.) See under {Ethereal}.

   {Glauber's salt} or {salts}. See in Vocabulary.

   {Haloid salt} (Chem.), a simple salt of a halogen acid, as
      sodium chloride.

   {Microcosmic salt}. (Chem.). See under {Microcosmic}.

   {Neutral salt}. (Chem.)
      (a) A salt in which the acid and base (in theory)
          neutralize each other.
      (b) A salt which gives a neutral reaction.

   {Oxy salt} (Chem.), a salt derived from an oxygen acid.

   {Per salt} (Old Chem.), a salt supposed to be derived from a
      peroxide base or analogous compound. [Obs.]

   {Permanent salt}, a salt which undergoes no change on
      exposure to the air.

   {Proto salt} (Chem.), a salt derived from a protoxide base or
      analogous compound.

   {Rochelle salt}. See under {Rochelle}.

   {Salt of amber} (Old Chem.), succinic acid.

   {Salt of colcothar} (Old Chem.), green vitriol, or sulphate
      of iron.

   {Salt of hartshorn}. (Old Chem.)
      (a) Sal ammoniac, or ammonium chloride.
      (b) Ammonium carbonate. Cf. {Spirit of hartshorn}, under
          {Hartshorn}.

   {Salt of lemons}. (Chem.) See {Salt of sorrel}, below.

   {Salt of Saturn} (Old Chem.), sugar of lead; lead acetate; --
      the alchemical name of lead being Saturn.

   {Salt of Seignette}. Same as {Rochelle salt}.

   {Salt of soda} (Old Chem.), sodium carbonate.

   {Salt of sorrel} (Old Chem.), acid potassium oxalate, or
      potassium quadroxalate, used as a solvent for ink stains;
      -- so called because found in the sorrel, or Oxalis. Also
      sometimes inaccurately called {salt of lemon}.

   {Salt of tartar} (Old Chem.), potassium carbonate; -- so
      called because formerly made by heating cream of tartar,
      or potassium tartrate. [Obs.]

   {Salt of Venus} (Old Chem.), blue vitriol; copper sulphate;
      -- the alchemical name of copper being Venus.

   {Salt of wisdom}. See {Alembroth}.

   {Sedative salt} (Old Med. Chem.), boric acid.

   {Sesqui salt} (Chem.), a salt derived from a sesquioxide base
      or analogous compound.

   {Spirit of salt}. (Chem.) See under {Spirit}.

   {Sulpho salt} (Chem.), a salt analogous to an oxy salt, but
      containing sulphur in place of oxygen.

Double \Dou"ble\, a. [OE. doble, duble, double, OF. doble,
   duble, double, F. double, fr. L. duplus, fr. the root of duo
   two, and perh. that of plenus full; akin to Gr. ? double. See
   {Two}, and {Full}, and cf. {Diploma}, {Duple}.]
   1. Twofold; multiplied by two; increased by its equivalent;
      made twice as large or as much, etc.

            Let a double portion of thy spirit be upon me. -- 2
                                                  Kings ii. 9.

            Darkness and tempest make a double night. --Dryden.

   2. Being in pairs; presenting two of a kind, or two in a set
      together; coupled.

            [Let] The swan, on still St. Mary's lake, Float
            double, swan and shadow.              --Wordsworth.

   3. Divided into two; acting two parts, one openly and the
      other secretly; equivocal; deceitful; insincere.

            With a double heart do they speak.    -- Ps. xii. 2.

   4. (Bot.) Having the petals in a flower considerably
      increased beyond the natural number, usually as the result
      of cultivation and the expense of the stamens, or stamens
      and pistils. The white water lily and some other plants
      have their blossoms naturally double.

   Note: Double is often used as the first part of a compound
         word, generally denoting two ways, or twice the number,
         quantity, force, etc., twofold, or having two.

   {Double base}, or {Double bass} (Mus.), the largest and
      lowest-toned instrument in the violin form; the
      contrabasso or violone.

   {Double convex}. See under {Convex}.

   {Double counterpoint} (Mus.), that species of counterpoint or
      composition, in which two of the parts may be inverted, by
      setting one of them an octave higher or lower.

   {Double court} (Lawn Tennis), a court laid out for four
      players, two on each side.

   {Double dagger} (Print.), a reference mark ([dag]) next to
      the dagger ([dagger]) in order; a diesis.

   {Double drum} (Mus.), a large drum that is beaten at both
      ends.

   {Double eagle}, a gold coin of the United States having the
      value of 20 dollars.

   {Double entry}. See under {Bookkeeping}.

   {Double floor} (Arch.), a floor in which binding joists
      support flooring joists above and ceiling joists below.
      See Illust. of Double-framed floor.

   {Double flower}. See {Double}, a., 4.

   {Double-framed floor} (Arch.), a double floor having girders
      into which the binding joists are framed.

   {Double fugue} (Mus.), a fugue on two subjects.

   {Double letter}.
      (a) (Print.) Two letters on one shank; a ligature.
      (b) A mail requiring double postage.

   {Double note} (Mus.), a note of double the length of the
      semibreve; a breve. See {Breve}.

   {Double octave} (Mus.), an interval composed of two octaves,
      or fifteen notes, in diatonic progression; a fifteenth.

   {Double pica}. See under {Pica}.

   {Double play} (Baseball), a play by which two players are put
      out at the same time.

   {Double plea} (Law), a plea alleging several matters in
      answer to the declaration, where either of such matters
      alone would be a sufficient bar to the action. --Stephen.

   {Double point} (Geom.), a point of a curve at which two
      branches cross each other. Conjugate or isolated points of
      a curve are called double points, since they possess most
      of the properties of double points (see {Conjugate}). They
      are also called {acnodes}, and those points where the
      branches of the curve really cross are called {crunodes}.
      The extremity of a cusp is also a double point.

   {Double quarrel}. (Eccl. Law) See {Duplex querela}, under
      {Duplex}.

   {Double refraction}. (Opt.) See {Refraction}.

   {Double salt}. (Chem.)
      (a) A mixed salt of any polybasic acid which has been
          saturated by different bases or basic radicals, as the
          double carbonate of sodium and potassium,
          {NaKCO3.6H2O}.
      (b) A molecular combination of two distinct salts, as
          common alum, which consists of the sulphate of
          aluminium, and the sulphate of potassium or ammonium.
          

   {Double shuffle}, a low, noisy dance.

   {Double standard} (Polit. Econ.), a double standard of
      monetary values; i. e., a gold standard and a silver
      standard, both of which are made legal tender.

   {Double star} (Astron.), two stars so near to each other as
      to be seen separate only by means of a telescope. Such
      stars may be only optically near to each other, or may be
      physically connected so that they revolve round their
      common center of gravity, and in the latter case are
      called also binary stars.

   {Double time} (Mil.). Same as {Double-quick}.

   {Double window}, a window having two sets of glazed sashes
      with an air space between them.

Source : WordNet®

double salt
     n : a solution of two simple salts that forms a single substance
         on crystallization