barrier

(noun): A structure that bars passage.
(noun): An obstacle or impediment.
(noun): A boundary or limit.
(noun): (grammar) A node (in government and binding theory) said to intervene between other nodes A and B if it is a potential governor for B, c-commands B, and does not c-command A.
(noun): A separation between two areas of the body where specialized cells allow the entry of certain substances but prevent the entry of others.
(noun): The lists in a tournament.
(noun): (in the plural) A martial exercise of the 15th and 16th centuries.
(verb): To block or obstruct with a barrier.