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]

WordNet (r) 3.0 (2006):

Tatar
    n 1: a member of the Mongolian people of central Asia who
         invaded Russia in the 13th century [syn: Tatar, Tartar,
         Mongol Tatar]
    2: a member of the Turkic-speaking people living from the Volga
       to the Ural Mountains (the name has been attributed to many
       other groups)
    3: the Turkic language spoken by the Tatar living from the Volga
       to the Ural Mountains

The Free On-line Dictionary of Computing (30 December 2018):

tatar

    A Turkic language spoken by about five
   million Tatars in Russia, Ukraine, Turkey and elsewhere; the
   official language of the Republic of Tatarstan (Russian
   Federation).

   language codes: tt, tat.

   (2006-12-11)