1. 圆的;圆形的
    Something that is circular is shaped like a circle.

circular

    e.g. ...a circular hole twelve feet wide and two feet deep...
           12英尺宽、2英尺深的圆坑
    e.g. Place your hands on your shoulders and move your elbows up, back, and down, in a circular motion.
           双手置于肩上，肘部向上、向后、向下做圆圈运动。

2. (旅程或路线)环行的，巡回的
    A circular journey or route is one in which you go to a place and return by a different route.

    e.g. Both sides of the river can be explored on this circular walk.
           沿着这条环行线路走一圈，河的两边都可以看到。

3. (论证或理论)循环论证的
    A circular argument or theory is not valid because it uses a statement to prove something which is then used to prove the statement.

4. (同时发送给很多人的)广告印刷品，通告
    A circular is an official letter or advertisement that is sent to a large number of people at the same time.

    e.g. The proposal has been widely publicised in BBC-TV press information circulars sent to 1,800 newspapers.
           在英国广播公司电视台发送给1,800家报社的新闻通报中，这项提议得到了广泛的宣传。