callous

The word 'callous' originates from the Latin callosus, meaning 'hard-skinned,' which itself derives from callum, signifying 'hardened skin' or a 'callus.' This literal sense transitioned into Middle English via Old French, initially describing physical toughness. By the 17th century, the meaning extended metaphorically to describe a person's emotional or mental insensitivity, drawing a direct analogy between unfeeling skin and an unfeeling disposition. Thus, the modern abstract meaning of being emotionally hardened or cruel evolved from a concrete physical description.

Structure: call (hard skin) + ous (adjective suffix) call (from Latin callum, meaning 'hardened skin'); ous (a suffix forming adjectives, from Latin -osus, meaning 'full of' or 'characterized by').