To strengthen or make hard; to become hard or callous.
From Old English 'heorten,' related to 'heart.' The word originally meant to make brave or courageous (from the heart), but evolved to mean making physically hard or emotionally callous by the Middle English period.
The word 'harten' reveals an old belief that courage and physical toughness come from the same place—the heart—which is why many old texts used 'harten' to describe both warriors becoming brave AND clay becoming hardened in fire.
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