Olympic refers to games, Olympian to a mountain. Olympic can also mean "pertaining to Mount Olympus," but careful users restrict its application to Olympia, a plain in ancient Greece where the Olympic Games were held in honor of the god Zeus. Olympian, by referring to the home of the gods of classical Greece, has come to mean "majestic," "superior," "aloof." "This valley has true Olympian beauty." "He was Olympian in his attitude toward money." "The Olympic Games of 1972 were held in Sapporo, Japan, and Munich, Germany."
Dictionary of problem words and expressions. Harry Shaw. 1975.