Made hard; hardened. (Dictionary.com)
Insensitive; indifferent; unsympathetic: (Dictionary.com)
Having a callus; indurated, as parts of the skin exposed to friction. (Dictionary.com)
If feet or hands are calloused, they are covered with hard areas of skin. (Cambridge Dictionary)
A foot or hand that is calloused is covered in calluses. (Collins Dictionary)
Why Crowds Make Us Callous.
Callous and unemotional traits show in brain structure of boys only, study finds.
Callous leadership – the leader and at least some followers are uncaring or unkind.