bulwark

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A wall or embankment raised as a defensive fortification; a rampart.
2. n. Something serving as a defense or safeguard: "We have seen the necessity of the Union, as our bulwark against foreign danger” ( James Madison).
3. n. A breakwater.
4. n. The part of a ship's side that is above the upper deck. Often used in the plural.
5. v. To fortify with a wall, embankment, or rampart.
6. v. To provide defense or protection for.

Century Dictionary and Cyclopedia

1. n. Originally, a barrier formed of logs, beams, boards, hurdles, or other materials, for the obstruction of a passage or defense of a place; now, specifically, in fortification, a rampart; a mound of earth carried around a place, capable of resisting cannon-shot, and formed with bastions, curtains, etc.; a fortification.
2. n. Nautical, a close barrier running around a ship or a part of it, above the level of the deck, and consisting of boarding nailed on the outside of the stanchions and timber-heads.
3. n. That which protects or secures against external annoyance or injury of any kind; a screen or shelter; means of protection and safety.
4. n. plural Pads or defenses to protect the limbs against the chafing of armor. Wright. Synonyms See fortification.
5. To fortify with a bulwark or rampart; secure by a fortification; protect.

Wiktionary

1. n. A defensive wall or rampart.
2. n. A defense or safeguard.
3. n. A breakwater.
4. n. nautical The planking or plating along the sides of a nautical vessel above her gunwale that reduces the likelihood of seas washing over the gunwales and people being washed overboard.
5. v. transitive To fortify something with a wall or rampart.
6. v. transitive To provide protection of defense for something.

GNU Webster's 1913

1. n. (Fort.) A rampart; a fortification; a bastion or outwork.
2. n. That which secures against an enemy, or defends from attack; any means of defense or protection.
3. n. (Naut.) The sides of a ship above the upper deck, usually a fencelike structure around the deck.
4. v. To fortify with, or as with, a rampart or wall; to secure by fortification; to protect.

WordNet 3.0

1. n. an embankment built around a space for defensive purposes
2. v. defend with a bulwark
3. n. a fencelike structure around a deck (usually plural)
4. n. a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away