Which term is used to describe the process of hardening into a semi-solid?

The term that describes the process of hardening into a semi-solid is "coagulate." This term is commonly used in contexts such as biology, cooking, and chemistry, where it refers to the process through which a liquid transforms into a solid or semi-solid state due to the aggregation of particles or proteins. For example, when blood coagulates, it forms clots, and when milk is heated, it can form curds through coagulation.

The other terms are unrelated to the process of hardening. "Collusion" refers to a secret agreement or cooperation between parties for a deceitful purpose. "Catharsis" is the process of releasing strong or repressed emotions, often related to psychological relief. "Cogent" means clear, logical, and convincing, typically in the context of arguments or reasoning. Thus, "coagulate" is the only term that accurately matches the concept of hardening into a semi-solid.