harden
verbUK /ˈhɑːdn/
US /ˈhɑːrdn/
To make something hard or become hard.
The clay will harden in the sun.
OTHER MEANINGS
2. To make someone stronger or less sensitive to pain or difficulty.
The training hardened the soldiers for battle.
3. To become more strict or determined.
Her face hardened when she heard the news.
4. To make a material or surface stronger and more resistant.
The steel is hardened by heating and cooling it quickly.