(1):
(n.) A fence or railing to mark the limits of a place, or to keep back a crowd.
(2):
(n.) An any obstruction; anything which hinders approach or attack.
(3):
(n.) A carpentry obstruction, stockade, or other obstacle made in a passage in order to stop an enemy.
(4):
(n.) A fortress or fortified town, on the frontier of a country, commanding an avenue of approach.
(5):
(n.) Any limit or boundary; a line of separation.