- the measure of a central angle subtending an arc equal in length to the radius: equal to 57.2958°. Abbreviation: rad
Origin of radian
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for radian
Historical Examples of radian
Strob, strob, n. the angular velocity of one radian per second.
- 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 angleSymbol: rad
Word Origin for radian
C19: from radius
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
"angle subtended at the center of a circle by an arc equal in length to the radius," 1879, from radius.
Online Etymology Dictionary, © 2010 Douglas Harper
- 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.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
- 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″.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.