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.) The sides of a ship above the upper deck.
To fortify with, or as with, a rampart or wall; to secure by fortification; to protect.