radian Meaning, Definition & Usage

  1. noun 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)
    rad.

WordNet

Ra"di*an noun
Etymology
From Radius.
Definitions
  1. (Math.) An arc of a circle which is equal to the radius, or the angle measured by such an arc.

Webster 1913