Crystallises means to form into crystals or to become rigid or fixed in a particular state. Synonyms for this word include congeals, solidifies, coagulates, freezes, sets, hardens, and petrifies. Congeals is often used to describe the process of a liquid becoming more solid, while solidifies more generally refers to the process of something becoming solid. Coagulates is frequently used in medical contexts to describe the clotting of blood or the curdling of milk. Freezes, sets, hardens, and petrifies all describe the process of becoming rigid or fixed, but each has a slightly different connotation. Overall, all of these words describe a similar process of transformation from a fluid or malleable state to a solid or fixed state.