- steradian [stə rā′dē ən]n.[ STE(REO)- + RADIAN]the basic unit of solid angular measure in the SI system, equal to the solid angle subtended at the center of a sphere by an area, on its surface, that is equal to the square of its radius: one sphere equals 4π steradians: abbrev. sr
English World dictionary. V. Neufeldt. 2014.