noun.
A barrier that protects a harbor or shore from the full impact of waves.
The Century Dictionary and Cyclopedia
noun.
Any structure or contrivance, as a mole, mound, wall, or sunken hulk, serving to break the force of waves and protect a harbor or anything exposed to the force of the waves.
the GNU version of the Collaborative International Dictionary of English
noun.
Any structure or contrivance, as a mole, or a wall at the mouth of a harbor, to break the force of waves, and afford protection from their violence.