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radian

[rey-dee-uh n] /ˈreɪ di ən/
noun, Mathematics.
1.
the measure of a central angle subtending an arc equal in length to the radius: equal to 57.2958°.
Abbreviation: rad.
Origin of radian
1875-1880
First recorded in 1875-80; radi(us) + -an
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for radian

radian

/ˈreɪdɪən/
noun
1.
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 angle rad
Word Origin
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
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Word Origin and History for radian
n.

"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
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radian in Medicine

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.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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radian in Science
radian
  (rā'dē-ən)   
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 © 2002. Published by Houghton Mifflin. All rights reserved.
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