bar·ri·er
[bar-ee-er]
noun
1.anything built or serving to bar passage, as a railing, fence, or the like: People may pass through the barrier only when their train is announced.
2.any natural bar or obstacle: a mountain barrier.
3.anything that restrains or obstructs progress, access, etc.: a trade barrier.
4.a limit or boundary of any kind: the barriers of caste.
5.Physical Geography . an antarctic ice shelf or ice front.
7. barriers, History/Historical . the palisade or railing surrounding the ground where tourneys and jousts were carried on.
8.Archaic . a fortress or stockade.