Quernstone refers to a grinding stone that is used for manually grinding grains or other materials. Some synonyms for quernstone include millstone, metate, and saddle quern. These words can be used interchangeably with quernstone to describe the same object. Millstone can refer to both the hand-operated grinding stone as well as larger, mechanical grinding stones that are found in mills. Metate is a Spanish word that describes a similar hand-held grinding stone used primarily in Central and South America. Saddle quern is a term used to describe a specific type of quernstone that has a saddle-shaped hollow for grinding. Overall, these synonyms provide different options for describing the same type of tool.