Bulwark (noun)

1. A defensive wall or rampart, especially one built around a castle or fort.
2. A person or thing that provides protection or support against attack or opposition.

Origin:

From the middle english word "bulwerke" which means a wall or a rampart built for defense.

Examples:

1. The castle's bulwark protected it from enemy attacks.
2. The bulwark of the ship is the part of the hull that is above the waterline.
3. She was a bulwark of support for her family during tough times.
4. The company's reputation was a bulwark against bad publicity.
5. The country's constitution is considered as a bulwark of democracy.