Tartar

noun

a member of the combined forces of central Asian peoples, including Mongols and Turks, who under the leadership of Genghis Khan conquered much of Asia and eastern Europe in the early 13th century, and under Tamerlane (14th century) established an empire with its capital at Samarkand.

from Old French Tartare or medieval Latin Tartarus, alteration (influenced by Tartarus) of Tatar.

noun

a hard calcified deposit that forms on the teeth and contributes to their decay.

late Middle English: via medieval Latin from medieval Greek tartaron, of unknown origin.