hard·en 
/ˈhɑɚdn̩/ verb
hard·ens; hard·ened; hard·en·ing /ˈhɑɚdn̩/ verb 1 : to become hard or firm or to make (something) hard or firm [no obj] ▪ It will take several hours for the concrete to harden (into a solid block). ▪ The gel hardens quickly. ▪ The presence of certain substances in the blood can cause the arteries to harden. [+ obj] ▪ These additives are designed to harden the steel. ▪ substances that can harden the arteries 2 : to become more definite and strongly felt or to make (something) more definite and strongly felt [no obj] ▪ Opposition to the goverment has hardened as news of further scandals has leaked out. [+ obj] ▪ The news has hardened opposition to the government. 3 [+ obj] : to make (someone) hard : to make (someone) less emotional and less likely to feel sorry for other people
▪ He had been hardened by his years of military service. 4 [no obj] : to begin to be or seem harsh, angry, serious, etc.
▪ Her voice/manner hardened as she spoke of her determination to win.
▪ He had been hardened by his years of military service.
▪ Her voice/manner hardened as she spoke of her determination to win.
harden your heart
◊If you harden your heart or if something hardens your heart, you stop having kind or friendly feelings for someone.
▪ She hardened her heart against him.
▪ She hardened her heart against him.
— hard·en·er /ˈhɑɚdnɚ/ noun, plural hard·en·ers [count]
▪ a metal hardener
/ˈhɑɚdnɚ/ noun, plural hard·en·ers [count] ▪ a metal hardener
— hardening noun [noncount]
▪ hardening of the arteries
▪ hardening of the arteries
