A defensive wall or rampart.
A defense or safeguard.
A breakwater.
Any means of defence or security.
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.
To give up, abandon or retire from something. To trade away.
To let go (free, away), physically release.
To metaphorically surrender, yield control or possession.
To accept to give up, withdraw etc.