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[rey-dee-uh n]
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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 .css-1fxfie5{font-size:22px;}@media (max-width:768px){.css-1fxfie5{font-size:18px;margin:0 10px 10px 0;word-break:break-all;word-wrap:break-word;-webkit-hyphens:auto;-moz-hyphens:auto;-ms-hyphens:auto;hyphens:auto;line-height:22px;}}radian

First recorded in 1875–80; radi(us) + -an
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for radian

Historical Examples

• Strob, strob, n. the angular velocity of one radian per second.

Chambers's Twentieth Century Dictionary (part 4 of 4: S-Z and supplements)

Various

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 angleSymbol: rad

Word Origin

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

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

(rādē-ən)
n.
1. 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.