harden
Definitions
To make or become firm, solid, or resistant to pressure.
To make or become physically or emotionally insensitive or callous.
To make something more capable of withstanding attack or adverse conditions.
Examples
The cold weather will harden the ground, making it difficult to dig.
Years of working in the harsh wilderness began to harden his outlook on life.
You should let the clay harden for twenty-four hours before painting it.