Definitions for Radianˈreɪ di ən
Random House Webster's College Dictionary
ra•di•anˈreɪ di ən(n.)
the measure of a central angle subtending an arc equal in length to the radius: equal to 57.2958°.
Ref: Abbr.: rad 2
Origin of radian:
the unit of plane angle adopted under the Systeme International d'Unites; equal to the angle at the center of a circle subtended by an arc equal in length to the radius (approximately 57.295 degrees)
In the International System of Units, the derived unit of plane angular measure of angle equal to the angle subtended at the centre of a circle by an arc of its circumference equal in length to the radius of the circle. Symbol: rad
Origin: From radi(us) + -an
an arc of a circle which is equal to the radius, or the angle measured by such an arc
The Standard Electrical Dictionary
The angle whose arc is equal in length to the radius; the unit angle.