The Collaborative International Dictionary of English v.0.48:

Bulwark \Bul"wark\, 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.
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         Of some proud city, bulwarked round and armed
         With rising towers.                      --Glover.
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The Collaborative International Dictionary of English v.0.48:

Bulwark \Bul"wark\, n. [Akin to D. bolwerk, G. bollwerk, Sw.
   bolwerk, Dan. bolv[aum]rk, bulv[aum]rk, 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.
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   2. That which secures against an enemy, or defends from
      attack; any means of defense or protection.
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            The royal navy of England hath ever been its
            greatest defense, . . . the floating bulwark of our
            island.                               --Blackstone.
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   3. pl. (Naut.) The sides of a ship above the upper deck,
      usually a fencelike structure around the deck.
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   Syn: See Rampart.
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WordNet (r) 3.0 (2006):

bulwark
    n 1: an embankment built around a space for defensive purposes;
         "they stormed the ramparts of the city"; "they blew the
         trumpet and the walls came tumbling down" [syn: rampart,
         bulwark, wall]
    2: a fencelike structure around a deck (usually plural)
    3: a protective structure of stone or concrete; extends from
       shore into the water to prevent a beach from washing away
       [syn: breakwater, groin, groyne, mole, bulwark,
       seawall, jetty]
    v 1: defend with a bulwark