barrier

Etymology

From Middle English barryer, barrere, barryȝer, from Old French barriere (compare French barrière), from Old French barre (“bar”).

noun

1. A structure that bars passage.
   The bus went through a railway barrier and was hit by a train.
   The bomber had passed through one checkpoint before blowing himself up at a second barrier.
2. An obstacle or impediment.
   Even a small fee can be a barrier for some students.
   America’s poverty line is $63 a day for a family of four. In the richer parts of the emerging world $4 a day is the poverty barrier. But poverty’s scourge is fiercest below $1.25 ([…]): people below that level live lives that are poor, nasty, brutish and short. 2013-06-01, “Towards the end of poverty”, in The Economist, volume 407, number 8838, page 11
3. A boundary or limit.
   Few marathon runners break the three-hour time barrier.
4. (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.
5. (physiology) A separation between two areas of the body where specialized cells allow the entry of certain substances but prevent the entry of others.
6. (historical) The lists in a tournament.
7. (historical, in the plural) A martial exercise of the 15th and 16th centuries.

verb

1. (transitive) To block or obstruct with a barrier.