The Collaborative International Dictionary of English v.0.48:

Tartar \Tar"tar\, n. [F. tartre (cf. Pr. tartari, Sp., Pg., &
   It. tartaro, LL. tartarum, LGr. ?); perhaps of Arabic
   origin.]
   1. (Chem.) A reddish crust or sediment in wine casks,
      consisting essentially of crude cream of tartar, and used
      in marking pure cream of tartar, tartaric acid, potassium
      carbonate, black flux, etc., and, in dyeing, as a mordant
      for woolen goods; -- called also argol, wine stone,
      etc.
      [1913 Webster]

   2. A correction which often incrusts the teeth, consisting of
      salivary mucus, animal matter, and phosphate of lime.
      [1913 Webster]

   Cream of tartar. (Chem.) See under Cream.

   Tartar emetic (Med. Chem.), a double tartrate of potassium
      and basic antimony. It is a poisonous white crystalline
      substance having a sweetish metallic taste, and used in
      medicine as a sudorific and emetic.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cream \Cream\ (kr[=e]m), n. [F. cr[^e]me, perh. fr. LL. crema
   cream of milk; cf. L. cremor thick juice or broth, perh. akin
   to cremare to burn.]
   1. The rich, oily, and yellowish part of milk, which, when
      the milk stands unagitated, rises, and collects on the
      surface. It is the part of milk from which butter is
      obtained.
      [1913 Webster]

   2. The part of any liquor that rises, and collects on the
      surface. [R.]
      [1913 Webster]

   3. A delicacy of several kinds prepared for the table from
      cream, etc., or so as to resemble cream.
      [1913 Webster]

   4. A cosmetic; a creamlike medicinal preparation.
      [1913 Webster]

            In vain she tries her paste and creams,
            To smooth her skin or hide its seams. --Goldsmith.
      [1913 Webster]

   5. The best or choicest part of a thing; the quintessence;
      as, the cream of a jest or story; the cream of a
      collection of books or pictures.
      [1913 Webster]

            Welcome, O flower and cream of knights errant.
                                                  --Shelton.
      [1913 Webster]

   Bavarian cream, a preparation of gelatin, cream, sugar, and
      eggs, whipped; -- to be eaten cold.

   Cold cream, an ointment made of white wax, almond oil, rose
      water, and borax, and used as a salve for the hands and
      lips.

   Cream cheese, a kind of cheese made from curd from which
      the cream has not been taken off, or to which cream has
      been added.

   Cream gauge, an instrument to test milk, being usually a
      graduated glass tube in which the milk is placed for the
      cream to rise.

   Cream nut, the Brazil nut.

   Cream of lime.
      (a) A scum of calcium carbonate which forms on a solution
          of milk of lime from the carbon dioxide of the air.
      (b) A thick creamy emulsion of lime in water.

   Cream of tartar (Chem.), purified tartar or argol; so
      called because of the crust of crystals which forms on the
      surface of the liquor in the process of purification by
      recrystallization. It is a white crystalline substance,
      with a gritty acid taste, and is used very largely as an
      ingredient of baking powders; -- called also potassium
      bitartrate, acid potassium tartrate, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cream of tartar
    n 1: a salt used especially in baking powder [syn: cream of
         tartar, tartar, potassium bitartrate, potassium
         hydrogen tartrate]