tartar / tarter [ˈtartɜr]
tartar – n. & v. – n. – 1. Chemistry bitartrate of potash (acid potassium tartrate), present in grape juice; 2. salts of tartaric acid; 3. any calcareous or other incrustation deposited from a liquid upon bodies in contact with it; 4. a deposit of calcium phosphate from the saliva, which tends to harden and concrete upon the teeth; 5. a rich fabric, probably silk, from the 15th and 16th centuries; 6. hell; v. – treat with a tartar emetic
tarter – adj. the comparative form of tart – 1. agreeably acidic, sharp or piquant taste; 2. marked by a biting, acrimonious, or cutting quality