The antonyms for the phrase "turn to liquid" include solidify, freeze, and harden. When a substance solidifies, it becomes firm and hard, losing its liquidity. Similarly, when a liquid freezes, it solidifies due to the reduction in temperature. Harden refers to the process of making something harder or firmer, often by cooling or drying. These terms are often used to describe substances like cement, chocolate, and wax, which undergo a change in their physical state. Turning something into a solid or hardening it can give it more stability and make it more useful for various purposes, such as construction or food processing.