Caulks or seals; to make something waterproof by filling cracks or gaps with material, or to fit a horse's shoe with calkins.
From caulk (to seal with caulk), which comes from Old French cauquer, from Latin calcare (to tread, press). Can also mean to fit calkins on a horse.
One word, 'calks,' can mean both sealing a ship to prevent it from sinking and adding grips to a horse's hoof to prevent it from falling—totally unrelated definitions that share an old root meaning 'to press.'
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