Which term refers to the hardening of a substance into a thicker form?

The term that refers to the hardening of a substance into a thicker form is coagulation. Coagulation is a process where a liquid or a substance transforms into a solid or semi-solid state, often through the aggregation of particles or the formation of a gel-like consistency. This process is commonly observed in biological contexts, such as blood clotting, where proteins aggregate to form a stable mass that helps stop bleeding. In culinary contexts, coagulation can be seen when milk curdles or when egg proteins set during cooking.

The other terms, while having defined meanings, relate to different concepts. Clamor refers to a loud and confused noise, often made by a group of people, and does not pertain to hardening. Coerce means to persuade someone to do something by using force or threats, which is unrelated to the concept of solidifying substances. A catalyst is a substance that speeds up a chemical reaction without being consumed in the process, which also does not relate to the hardening or thickening of materials. Hence, coagulation is the correct choice as it directly describes the phenomenon of a substance changing from a liquid to a more solid form.