The unit of solid angle; the solid angle that encloses an area on the surface of a sphere equivalent to the square of the radius of the sphere. [G. stereos, solid, + radion, radius]
* * *
ste·ra·di·an sti-'rād-ē-ən n a unit of measure of solid angles that is expressed as the solid angle subtended at the center of the sphere by a portion of the surface whose area is equal to the square of the radius of the sphere
* * *
ste·ra·di·an (sr) (stə-raґde-ən) [Gr. ster- solid + radian] the SI unit of measurement of solid angles, equivalent to the angle subtended at the center of a sphere by an area on its surface equal to the square of its radius. A full sphere subtends 4π steradians.Medical dictionary. 2011.