Plural of calkin; metal grips or points attached to a horse's shoe to prevent slipping on ice or wet ground.
Variant of caulkin/caukin, possibly from Old Norse kálkinn or related to 'calk.' The devices became standard for horses working in winter conditions in northern climates.
Before snowplows, calkins were how civilization continued through winter—without them on horses' hooves, medieval and early modern towns would grind to a halt when snow came.
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