What is callus? How to use in English

The word "callus" is derived from the Latin word "callus" meaning rough or hard. In Roman times, the term was primarily used to describe a hardened or thickened area on plant stems, bark, or leaves. The use of the word "callus" to describe similar conditions in humans can be traced back to the 16th century when medical terms based on Latin were introduced. This new meaning, describing a thickened, rough, or hardened area of skin, particularly on the hands and feet, is attributed to anatomist Thomas Caius. The word "callus" quickly gained popularity in medical circles due to its descriptive quality. The term's use expanded beyond medical vocabulary in the 19th century, when the roots of modern sports began to take shape. "Callous" or adjectives like "callously" began to be used figuratively to describe actions as hard and unfeeling as the calluses that were forming on athletes' feet. Today, "callus" is a commonly used word in both medical and popular discourse, and its Latin roots remain evident. The term continues to be used for thickened, hardened skin in humans, as well as in describing similar conditions in plants.