* Solidify: This is a direct opposite, meaning to become solid or firm.
* Freeze: This is the specific opposite of melting ice or water.
* Harden: This means to become strong and firm, often by cooling or drying.
* Congeal: This refers to the process of a liquid becoming thick or solid.
* Form: This is a broader term that can indicate the opposite of melting, such as forming into a shape or structure.
The best antonym for "melt" will depend on the specific situation.