Which verb means to combine or unite to make something solid or firm?

The verb that means to combine or unite to make something solid or firm is "consolidate." This term specifically refers to the act of merging or bringing together elements to create a more stable, unified whole. In various contexts, such as in business or finance, consolidation often involves combining resources, companies, or data to enhance efficiency and strength.

The other choices do not convey this meaning. "Integrate" also suggests combining but often focuses on the inclusion of parts into a whole rather than the process of making something solid or firm. "Separate" and "divide" imply a breaking apart or disconnecting of elements, which is the opposite of combining or uniting. Hence, "consolidate" is the most accurate choice for the given definition.