stadiumyoudaoicibaDictYouDict[stadium 词源字典]
stadium: [16] Greek stádion denoted a ‘racetrack’, particularly the one at Olympia, which was about 185 metres long. In due course the word came to be used as a term for a measure of length equal to this, and that was the sense in which English originally acquired it, via Latin stadium. The original ‘racetrack’ was introduced in the 17th century, and ‘sports arena’ is a modern development of this. The Greek word itself was an alteration of an earlier spádion ‘racetrack’, a derivative of span ‘pull’ (source of English spasm). The change from sp- to st- was perhaps set in motion by Greek stádios ‘fixed, firm’.
=> spasm[stadium etymology, stadium origin, 英语词源]
stadium (n.)youdaoicibaDictYouDict
late 14c., "a foot race; an ancient measure of length," from Latin stadium "a measure of length; a course for foot-racers" (commonly one-eighth of a Roman mile or a little over 600 English feet; translated in early English Bibles by furlong), from Greek stadion "a measure of length; a race-course, a running track," especially the track at Olympia, which was one stadion in length. The meaning "running track," recorded in English from c. 1600, was extended to mean in modern-day context "large, open oval structure with tiers of seats for viewing sporting events" (1834).

"Originally the distance between successive stations of the shouters and runners employed to estimate distances" [Century Dictionary]. According to Barnhart, the Greek word might literally mean "fixed standard of length" (from stadios "firm, fixed," from PIE root *sta- "to stand"), or it may be from spadion, from span "to draw up, pull," with form influenced by stadios.