callous
"Callous" is a word with two related meanings — one literal (about skin) and one figurative (about personality). The figurative sense is by far the more common one you'll encounter in everyday English.
When someone is callous, they show no sympathy or concern for other people's feelings or suffering. Imagine a person who sees someone crying and just shrugs and walks away — that's a callous reaction. It suggests a kind of hardness on the inside, like nothing touches them emotionally.
everyday language, describing personality or behavior · Modern, widely used · figurative
In a very literal, physical sense, callous describes skin that has become thick and hard — usually because of repeated rubbing or pressure. A guitarist's fingertips or a carpenter's hands often become callous over time. This is the original meaning of the word, and it gave rise to the figurative sense above.
medicine, everyday language · Used in both older and modern texts, but less common in conversation