Thicken is a verb that is commonly used to describe the process of making something more viscous or dense. However, depending on the context in which it is used, there are various synonyms that can be used in its place. Some of the most common synonyms for thicken include "congeal," "coagulate," "gel," "solidify," and "harden." These words are often used in cooking or chemistry contexts to describe the process of turning liquids or gels into solids. Other synonyms for thicken include "deepen," "intensify," "strengthen," and "amplify." These words are often used in more abstract contexts, such as emotions or relationships, to describe the process of making something stronger or more powerful.