Merriam-Webster Collegiate Dictionary - stadium

 noun  (plural stadia or -diums)  Etymology: Middle English, from Latin, from Greek stadion  Date: 14th century  1.  a. any of various ancient Greek units of length ranging in value from 607 to 738 feet (about 185 to 225 meters)  b. an ancient Roman unit of length equal to 607 feet (185 meters)  2.  a. a course for footraces in ancient Greece originally one ~ in length  b. a tiered structure with seats for spectators surrounding an ancient Greek running track  c. a large usually roofless building with tiers of seats for spectators at sports events  3. New Latin, from Latin a stage in a life history; especially one between successive molts of an insect