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