The Collaborative International Dictionary of English v.0.48:

Olympic games \O*lym"pic games\, or Olympian games \O*lym"pi*an
games\ . (Greek Antiq.),
   The greatest of the national festivals of the ancient Greeks,
   consisting of athletic games and races, dedicated to Olympian
   Zeus, celebrated once in four years at Olympia, and
   continuing five days.
   [1913 Webster] Olympic games

WordNet (r) 3.0 (2006):

Olympian Games
    n 1: the ancient Panhellenic celebration at Olympia in honor of
         Zeus; held every 4 years beginning in 776 BC [syn:
         Olympian Games, Olympic Games]