The Collaborative International Dictionary of English v.0.48:

Tartar \Tar"tar\, n.
   1. [Per. T[=a]t[=a]r, of Tartar origin.] A native or
      inhabitant of Tartary in Asia; a member of any one of
      numerous tribes, chiefly Moslem, of Turkish origin,
      inhabiting the Russian Europe; -- written also, more
      correctly but less usually, Tatar.
      [1913 Webster]

   2. A person of a keen, irritable temper.
      [1913 Webster]

   To catch a tartar, to lay hold of, or encounter, a person
      who proves too strong for the assailant. [Colloq.]
      [1913 Webster]

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.
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   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:

Tartar \Tar"tar\, a.
   Of or pertaining to Tartary in Asia, or the Tartars.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tartar \Tar"tar\, n. [Cf. F. tartare.]
   See Tartarus. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tartar
    n 1: a salt used especially in baking powder [syn: cream of
         tartar, tartar, potassium bitartrate, potassium
         hydrogen tartrate]
    2: a fiercely vigilant and unpleasant woman [syn: dragon,
       tartar]
    3: a member of the Mongolian people of central Asia who invaded
       Russia in the 13th century [syn: Tatar, Tartar, Mongol
       Tatar]
    4: an incrustation that forms on the teeth and gums [syn:
       tartar, calculus, tophus]