noun

A "moat" is a deep, wide ditch filled with water that surrounds a castle or fort, often serving as a defense against attackers. It can also be dry, but its primary purpose is to provide protection.

Example

1. The castle was surrounded by a moat to protect it from attack.
2. The moat was filled with water to make it difficult for enemies to cross.
3. The moat was a symbol of the power and wealth of the castle's owner.