radian ra·di·an (rā'dē-ən)
n.
Abbr. rad
A unit of angular measure equal to the angle subtended at the center of a circle by an arc equal in length to the radius of the circle.
radian (rā'dē-ən) Pronunciation Key
A supplementary unit of the International System used in angular measure. One radian is equal to the angle subtended at the center of a circle by an arc equal in length to the radius of the circle, approximately 57°17'44.6". |