adjective
1. insensitive; unfeeling; hardhearted.
Their unwillingness to help showed a callous disregard for the suffering of others.
The war had made the him callous, and he felt no sympathy for the plight of the villagers.
2. having calluses; hardened; thickened.
She saw from his callous hands that he’d been hard at work in the garden.
transitive & intransitive verb
to become or cause to become callous.
The long marches calloused the soldier’s feet.