Extract from the FREE DICTIONARY: Calk
1. A pointed extension on the toe or heels of a horseshoe, designed to prevent slipping.
2. A spiked plate fixed on the bottom of a shoe to prevent slipping and preserve the sole.
[Probably back-formation from obsolete calkin, from Middle English kakun, possibly from Middle Dutch kalkoen, hoof, or from Old French calcain, heel (Middle Dutch, from Old French), from Latin calcneum, heel bone;