Any means of defence or security.
A defensive wall or rampart.
A defense or safeguard.
A breakwater.
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.
To fortify something with a wall or rampart.
To provide protection of defense for something.
Something serving as a security for such an undertaking.
An assurance or guarantee.
An undertaking to answer for the payment of some debt, or the performance of some contract or duty, of another, in case of the failure of such other to pay or perform; a warranty; a security.