American Dictionary of the English Language

BREAKWATER, noun [break and water.] The hull of an old vessel sunk at the entrance of a harbor, to break or diminish the force of the waves, to secure the vessels in harbor.

1. A small buoy fastened to a large one, when the rope of the latter is not long enough to reach the surface of the water.

2. A mole, at the mouth of a harbor, intended to break the force of the waves.