steradian

UK: /stəˈreɪdɪən/ US: (stə rā′dē ən)

WordReference Random House Unabridged Dictionary of American English © 2025

ste•ra•di•an  (stə rā′dē ən), n. [Geom.]

1. Mathematics a solid angle at the center of a sphere subtending a section on the surface equal in area to the square of the radius of the sphere. Abbr.: sr

• ste(reo)- + radian 1880–85

Collins Concise English Dictionary © HarperCollins Publishers::

steradian / stəˈreɪdɪən/ noun

1. an SI unit of solid angle; the angle that, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to the square of the length of the radius
   Symbol: sr

Etymology: 19th Century: from stereo- + radian