Made hard or firm through a process; toughened physically or emotionally; became callous or unfeeling. Past participle of 'harden.'
From 'hard' (Old English 'heard' meaning 'solid, firm') + '-en' suffix indicating process of becoming. The figurative sense of emotional toughening developed alongside the physical meaning by 1500s.
The journey from soft to hard captures one of life's fundamental transformations - whether it's steel in a forge, calluses on hands, or hearts that protect themselves through experience. Remarkably, the same process that makes materials stronger can make people less emotionally flexible.
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