What is a thin paste made from water or stock mixed with starch called?

A thin paste made from water or stock mixed with starch is called a slurry. This mixture serves as a thickening agent for soups, sauces, and gravies. When the starch is added to the liquid and heated, it expands and gels, which thickens the consistency of the dish to which it is added. Slurries are typically made with cornstarch, potato starch, or other starches that dissolve easily in liquid.

By contrast, a roux is a cooked mixture of equal parts fat and flour used as a thickening agent, while gravy is a sauce often made by thickening a liquid (usually meat drippings) with a starch or roux. A paste, while similar, does not specifically refer to the mixture with stock or water and starch and lacks the precise application and usage that defines a slurry. Therefore, the details of the composition and intended use make "slurry" the correct term in this context.