Bulwark, n.
Etymology: [Akin to D. bolwerk, G. bollwerk, Sw. bolwerk, Dan. bolvärk, bulvärk, rampart; akin to G. bohle plank, and werk work, defense. See Bole stem, and Work, n., and cf. Boulevard.]
1. (Fort.)
A rampart; a fortification; a bastion or outwork.
2. That which secures against an enemy, or defends from attack; any means of defense or protection. The royal navy of England hath ever been its greatest defense, . . . the floating bulwark of our island. Blackstone.
3. pl. (Naut.)
2 more senses
The sides of a ship above the upper deck.
Syn. -- See Rampart.
1 other Webster entry under this spelling
Bulwark, v. t. [imp. & p. p. Bulwarked (; p. pr. & vb.n. Bulwarking.]
To fortify with, or as with, a rampart or wall; to secure by fortification; to protect. Of some proud city, bulwarked round and armed With rising towers. Glover.
Shades of meaning
Fernald has no entry of its own for bulwark; he lists it under barrier, defense.
Where he writes about it:
Bulwark is a general word for any defensive wall or rampart; its only technical use at present is in nautical language, where it signifies the raised side of a ship above the upper deck, topped by the rail. — from barrier