1. 障碍；壁垒；阻碍
    A barrier is something such as a rule, law, or policy that makes it difficult or impossible for something to happen or be achieved.

barrier的翻译

    e.g. Duties and taxes are the most obvious barrier to free trade.
           关税和税收是自由贸易的最大壁垒。

2. 隔阂；阻碍
    A barrier is a problem that prevents two people or groups from agreeing, communicating, or working with each other.

    e.g. There is no reason why love shouldn't cross the age barrier...
           爱没有理由不能跨越年龄的阻碍。
    e.g. She had been waiting for Simon to break down the barrier between them...
           她一直在等待西蒙打破他们之间的隔阂。

3. 关卡；栅栏
    A barrier is something such as a fence or wall that is put in place to prevent people from moving easily from one area to another.

    e.g. The demonstrators broke through heavy police barriers...
           示威者们冲破了警察的重重设防。
    e.g. As each woman reached the barrier one of the men glanced at her papers.
           每一位女士来到关卡前，其中一个男士便会扫一眼她的证件。

4. 障碍物；挡板；屏障
    A barrier is an object or layer that physically prevents something from moving from one place to another.

barrier的反义词

    e.g. ...a severe storm, which destroyed a natural barrier between the house and the lake...
           猛烈的暴风雨摧毁了房子和湖之间的一道天然屏障
    e.g. The packaging must provide an effective barrier to prevent contamination of the product.
           包装必须提供有效的保护，以免产品受污染。

5. 大关；界限
    You can refer to a particular number or amount as a barrier when you think it is significant, because it is difficult or unusual to go above it.

    e.g. They are fearful that unemployment will soon break the barrier of three million...
           他们担心失业人数很快将突破300万大关。
    e.g. The Popular Front failed, as expected, to pass the 5 per cent barrier.
           不出所料，人民阵线没能突破5%大关。

6. see also: crash barrier;sound barrier