Fluidifying is a process of making something more fluid or liquid-like. The opposite of fluidifying, therefore, would be to make something less liquid or more solid. Some antonyms for the word fluidifying could include solidifying, hardening, firming, thickening, coagulating, or congealing. These terms are often used in relation to substances such as liquids or gels, and can refer to processes such as cooling, evaporation, or mixing with certain ingredients. For example, a recipe may call for the addition of a thickening agent to prevent a sauce from fluidifying too much, or a metal may need to be solidified by cooling it down in order to hold its shape.