柯林斯詞典radian /?re?d??n/ 1. N an SI unit of plane angle; the angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius. 1 radian is equivalent to 57.296 degrees and π/2 radians equals a right angle 弧度 ( symbol: rad) 返回 radian劍橋詞典the measure of an angle at the centre of a circle opposite an arc (= part of the edge of a circle ) that is the same length as the radius (= the line from the centre to the edge of the circle ) 弧度 返回 radian