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tartar (TAHR tuhr) (noun)
1. A hard yellowish deposit on the teeth, consisting of organic secretions and food particles deposited in various salts, such as calcium carbonate: "The dental hygienist used a sharp tool to clean the tartar off my teeth."
2. A reddish acid compound, chiefly potassium bitartrate, found in the juice of grapes and deposited on the sides of casks during wine-making process: "During the making of wine, the workers watch carefully for the sedimentation of tartar in the barrels they use."
3. An individual described as having an unpredictable temper (considered informal and old-fashioned): "She was a perfect tartar when she was crossed by her intrusive editor."
Tartar (TAHR tuhr) (noun)
A member of any of the Turkic and Mongolian people of central Asia who invaded Western Asia and Eastern Europe in the Middle Ages: "The Tartar invaders were believed to be superb horsemen."

The old history book described the Tartar as being a tartar in terms of temperament. Perhaps the teeth of the Tartar hurt because of a build up of tartar in his mouth that made him miserable all the time.