steradian

/S T EH0 R EY1 D IY0 AH0 N/
noun
  1. 1

    In the International System of Units, the derived unit of solid angle; the solid angle subtended at the centre of a sphere of radius r by a portion of the surface of the sphere that has area r2. Symbol: sr

Synonyms

Source: https://en.wiktionary.org/wiki/steradian