radian

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″.

The angle subtended at the center of a circle by an are equal in length to the radius. Also called the unit angle in circular measure. It is equal to 57° 17′ 44″. 80625 nearly.

A unit of angular velocity equivalent, approximately, to 0.15916 revolutions per second, or, strictly, to revolutions per second: in full, radian per second.

An arc of a circle which is equal to the radius, or the angle measured by such an arc.

In the International System of Units, the derived unit of plane angular measure of angle equal to the angle subtended at the centre of a circle by an arc of its circumference equal in length to the radius of the circle. Symbol: rad

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)