Meaning of radian

ra•di•an

Pronunciation: (rā'dē-un), [key]
— n. Math.
  1. the measure of a central angle subtending an arc equal in length to the radius: equal to 57.2958°. Abbr.: rad
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
See also:
radial triangulation radiance