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When the length of an arc of a circle is equal to the radius of the circle, the angle subtended by that arc equals one radian.
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, approximately 57°17′44.6".
(Units) 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. Symbol: rad
[C19: from radius]
ra•di•an(ˈreɪ di ən)
the measure of a central angle subtending an arc equal in length to the radius: equal to 57.2958°. Abbr.: rad
A unit of angular measure equal to a little more than 57°. This is the measure of an angle whose vertex is the center of a circle and whose two rays intersect the circle so as to form an arc with the same length as the circle's radius.
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|Noun||1.||radian - 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)|
angular unit - a unit of measurement for angles
milliradian - a unit of angular distance equal to one thousandth of a radian