any line in a plane figure which divides the figure into two such parts that one part, when folded over along the axis, shall coincide with the other part.
双语例句
The graph is divided by its symmetry axis. 这个图形沿着对称轴左右对称。
Most of the characters we use in our daily writing do not have axes of symmetry. 我们日常使用的文字大部分没有对称轴。
