barrier

noun

• a fence or other obstacle that prevents movement or access.
• a circumstance or obstacle that keeps people or things apart or prevents communication or progress:a language barrier the cultural barriers to economic growth
• the starting gate of a racecourse.
• British a gate at a parking lot that controls access by being raised or lowered.
• (in full barrier island) a long narrow island lying parallel and close to the mainland, protecting the mainland from erosion and storms.