1. 柏油;沥青
    Tar is a thick black sticky substance that is used especially for making roads.

    e.g. The oil has hardened to tar...
           油已经硬化成柏油了。
    e.g. They drove across the river to New Hampshire on a hot tar road.
           他们沿着一条滚烫的柏油路开过了河，来到新罕布什尔州。

2. (烟草中的)焦油
    Tar is one of the poisonous substances contained in tobacco.

3. 被当作一丘之貉;被当成一路货色
    If some people in a group behave badly and if people then wrongly think that all of the group is equally bad, you can say that the whole group is tarred with the same brush .

tar的近义词

    e.g. I am a football supporter and I have to often explain that I'm not one of the hooligan sort because we'll all get tarred with the same brush when there's trouble.
           我是足球迷，经常要解释我不是那种足球流氓，因为一旦出事，我们就会被当成是一路货色。

4. see also: tarred