A rope or cable attached to a ship's breast (front), used for mooring or anchoring.
Compound: 'breast' (front of ship) + 'fast' (a nautical rope). 'Fast' in nautical terminology means a rope securing a vessel, from Old Norse 'fastr' (secure).
Medieval sailors had dozens of specialized ropes, each with its own name describing exactly where it attached—the 'breastfast' told you immediately 'this rope holds the front of the ship.' It's like using one word instead of a whole instruction manual!
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