Source : Webster's Revised Unabridged Dictionary (1913)

Stadium \Sta"di*um\, n.; pl. {Stadia}. [L., a stadium (in sense
   1), from Gr. ?.]
   1. A Greek measure of length, being the chief one used for
      itinerary distances, also adopted by the Romans for
      nautical and astronomical measurements. It was equal to
      600 Greek or 625 Roman feet, or 125 Roman paces, or to 606
      feet 9 inches English. This was also called the {Olympic
      stadium}, as being the exact length of the foot-race
      course at Olympia. --Dr. W. Smith.

   2. Hence, a race course; especially, the Olympic course for
      foot races.

   3. A kind of telemeter for measuring the distance of an
      object of known dimensions, by observing the angle it
      subtends; especially (Surveying), a graduated rod used to
      measure the distance of the place where it stands from an
      instrument having a telescope, by observing the number of
      the graduations of the rod that are seen between certain
      parallel wires (stadia wires) in the field of view of the
      telescope; -- also called {stadia}, and {stadia rod}.