A real or imaginary line about which something rotates or is symmetric

物体旋转或呈对称排列所依的真实或假想直线

A reference line in a coordinate system or graph for locating values

坐标系或图表中用于定位数值的参考轴线

The second cervical vertebra, enabling rotation of the head

第二颈椎（C2），使头部得以旋转

The main stem or central structure of a plant

植物的主轴或中心结构

The central line or focus around which activity is organized

活动围绕其组织的中心线或核心