The Collaborative International Dictionary of English v.0.48:
Stadium \Sta"di*um\ (st[=a]"d[i^]*[u^]m), n.; pl. Stadia
(st[=a]"d[i^]*[.a]). [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
3. Hence: A modern structure, with its inclosure, resembling
the ancient stadium, used for athletic games which are
typically played out-of-doors; such stadiums are usually
large structures without roofs, though some modern
stadiums may have a protective dome overhead. It may be
contrasted with the arena, the term commonly used for
smaller structures at which indoor games are played.
[Webster 1913 Suppl. +PJC]
4. 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.